Singtel Wifi calling

[xiaofan]

Interestingly WiFi calling (VoWiFi) works with the StarHub Prepaid S plan on a very old iPhone 7+ 256GB version phone (bought in late 2016) running iOS 15.8.5.

BTW, it is good that Apple still provides software patches for this old iPhone.

Original: iOS 10.0.1
Current: iOS 15.8.5, released on September 15, 2025

 

[xiaofan]

Just tested an M1 Prepaid Card and it works with VoWiFi on Poco X6 Pro.

Summary of my test results:

1. Xiaomi Poco Android phones

Xiaomi Poco C85 4G Phone --> released in Sept 2025
Eight 4G SIM works with with WiFi Calling (VoWiFi).

XIaomi Poco X7 Pro 5G Phone --> released in Jan 2025
Singtel SIM Only 5G SIM and M1 Maxx 5G SIM work with WiFi Calling (VoWiFi).
SIMBA 5G SIM does not work with VoWiFi.

XIaomi Poco X6 Pro 5G Phone --> released in Jan 2024
Singtel SIM Only 5G SIM, M1 Maxx 5G SIM and M1 Prepaid Card 5G SIM work with WiFi Calling (VoWiFi).
Eight 4G SIM and SIMBA do not work with VoWiFi.

Xiaomi Poco X4 GT 5G Phone --> released in June 2022
Starhub Prepaid S 5G SIM does not work with VoWiFi.

2. Apple iPhones
iPhone 14 (5G phone) --> released in Sept 2022
Singtel SIM Only 5G SIM works with WiFi Calling (VoWiFi).

iPhone 7+ (4G phone) --> released in Sept 2016
Starhub Prepaid S Plan 5G SIM works with WiFi Calling (VoWiFi).

 

[A7997A]

Interestingly WiFi calling (VoWiFi) works with the StarHub Prepaid S plan on a very old iPhone 7+ 256GB version phone (bought in late 2016) running iOS 15.8.5.

BTW, it is good that Apple still provides software patches for this old iPhone.

Original: iOS 10.0.1
Current: iOS 15.8.5, released on September 15, 2025

iPhone generally have very good support for telephony features, including VoWifi.
Their VoWifi support is one of the best around, the exception is Simba.

 

[xiaofan]

Tested Circles.Life 5G three months free trial plan and it does not work with VoWiFi, tested using Poco X7 Pro.

For Poco X7 Pro dual SIM Configuration (two phones).
1) SingTel SIM Only on SIM 1 and M1 Maxx 5G on SIM 2, VoWiFi works on both SIMs but sometimes SIM2 VoWiFi will drop.

2) SingTel SIM Only on SIM 1 and CUniq 4G on SIM 2, VoWiFi works on both SIMs. Not tested long enough but probably SIM2 VoWiFi may drop.

3) SIMBA on SIM1 and Eight 4G on SIM2, SIMBA VoWiFi is known not to work with Poco X7 Pro. So far Eight 4G on SIM2 seems to work fine with VoWiFi.

 

[froztheart]

Data point for future reference.

VoWIFI working on Pixel with ST (MNO) SIM.
VoWIFI working on my iPhones too now.


iPhone-Specific Issues

• Software Glitches and Bugs: Recent iOS updates can sometimes introduce bugs that affect Wi-Fi calling functionality.
• Incorrect Settings:
  • VoWiFi/Wi-Fi Calling is off: The feature must be explicitly enabled in Settings > Phone > Wi-Fi Calling.
  • Airplane Mode with Wi-Fi enabled: Forcing VoWiFi often works best when the iPhone is in Airplane Mode with Wi-Fi manually toggled back on, ensuring no cellular interference.
  • Wi-Fi Assist Enabled: This feature automatically switches to cellular data when Wi-Fi is weak, which can interrupt VoWiFi calls as the phone bounces between networks. It's recommended to turn it off in Settings > Cellular.
  • VPN Interference: An active VPN connection can block the specific ports needed for Wi-Fi calling. Deleting the VPN profile completely may be necessary.
  • Incorrect Date & Time: Ensuring the "Set Automatically" option is enabled in Settings > General > Date & Time is crucial for proper call routing.
  • Carrier Settings Update: Outdated carrier settings can cause issues. These updates usually happen automatically, but manual checks are sometimes needed.
• Physical Interference: Bulky, non-standard, or metallic phone cases can weaken the Wi-Fi signal reception.

Network and Infrastructure Issues

• Weak or Unstable Wi-Fi Signal: VoWiFi requires a strong, consistent internet connection. Being too far from the router or having physical obstructions (walls, metal, large furniture) can degrade call quality.
• Router/ISP Issues:
  • Network Congestion: Too many devices using the network simultaneously can cause a bottleneck, affecting call quality.
  • Router Configuration: Some routers may not be configured to prioritize latency-sensitive VoIP traffic, or may block necessary ports.
  • Incompatible Networks: Not all Wi-Fi networks (especially public ones) support the protocols necessary for VoWiFi.
• Bouncing Signals: A primary cause of call drops occurs when the iPhone struggles to hand off seamlessly between a weak cellular signal and a Wi-Fi signal. If both are present, the phone may repeatedly try to switch, interrupting the call.
• Carrier Limitations: The mobile service provider must support Wi-Fi calling for your specific device and plan. Sometimes the issue lies with the carrier's network infrastructure or their implementation of the service.

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NEW ONT replaced by ISP, replaced NEW ASUS routers, stock firmwares without any changes in settings out of the box.

Okay, tested across my devices and my findings are:

Forcing VoWIFI (Tested on both WIFI network @ residence to ensure not ISP/Router issue)
WIFI Assist - OFF
Airplane Mode - ON
iPhone 16PM (IOS 26.1) - M1 & MY (Roaming on SIMBA) SIM both reflected VoWIFI
iPhone 13PM (IOS 18.7.1) - ST & MR SIM, ONLY ST SIM reflected VoWIFI
iPhone 12P (IOS 18.7.1) - SH & MY SIM (Roaming on Starhub), ONLY MY SIM reflected VoWIFI

Noticed that VoWIFI is lost once Cellular is established back, while secondary SIM's VoWIFI remains (for MY SIM, yet to test out with M1/ST as secondary SIM).

Also, seems like VoWIFI doesn't work on Starhub from the test I conducted across Starhub (MNO), MR & CUniq (MVNOs) since all does not reflect VoWIFI.
Going to check with Starhub for further clarification.

 

[xiaofan]

Also, seems like VoWIFI doesn't work on Starhub from the test I conducted across Starhub (MNO), MR & CUniq (MVNOs) since all does not reflect VoWIFI.
Going to check with Starhub for further clarification.

I have tested the following on my Poco phones and all three are working.

StarHub Prepaid S 5G on Poco X4 GT
Eight 4G (SIM2) on Poco X7 Pro
CUniq 4G (SIM2) on Poco X7 Pro

Then I have also tested StarHub Prepaid S on old iPhone 7+ and VoWiFi works as well.

 

[xiaofan]

VoWiFi on Poco X7 Pro.
SIM 1 -- Singtel SIM Only Plan
SIM 2 -- CUniq 4G S$9.9 plan (ported from M1 Maxx S$10 plan, for better China roaming data bundle).

VoWiFi works across the following three use cases. But as per the reports, SIM 2 VoWiFi may drop and that was the case when I was using Singtel SIM Only and M1 Maxx. But so far I have not seen SIM 2 drops VoWiFi with the current combination.

1) Normal use case

2) Turn off Data

3) Airplane mode with WiFi only

 

[froztheart]

I have tested the following on my Poco phones and all three are working.

StarHub Prepaid S 5G on Poco X4 GT
Eight 4G (SIM2) on Poco X7 Pro
CUniq 4G (SIM2) on Poco X7 Pro

Then I have also tested StarHub Prepaid S on old iPhone 7+ and VoWiFi works as well.

Hmmm... that's werid since all Starhub didn't work on my iPhone when I tested...

VoWiFi on Poco X7 Pro.
SIM 1 -- Singtel SIM Only Plan
SIM 2 -- CUniq 4G S$9.9 plan (ported from M1 Maxx S$10 plan, for better China roaming data bundle).

VoWiFi works across the following three use cases. But as per the reports, SIM 2 VoWiFi may drop and that was the case when I was using Singtel SIM Only and M1 Maxx. But so far I have not seen SIM 2 drops VoWiFi with the current combination.

1) Normal use case

2) Turn of Data

3) Airplane mode with WiFi only

Yeah, Android do not seem to be an issue on my end too.
Not sure what else might be the issue that's causing Starhub to not reflect VoWIFI on my iPhone.

You tested on your iPhone if VoWIFI is working on Starhub?

 

[xiaofan]

Hmmm... that's werid since all Starhub didn't work on my iPhone when I tested...

Yeah, Android do not seem to be an issue on my end too.
Not sure what else might be the issue that's causing Starhub to not reflect VoWIFI on my iPhone.

You tested on your iPhone if VoWIFI is working on Starhub?

Yes, please refer to earlier report from my side, for StarHub Prepaid S plan (5G), VoWiFi works fine on an old iPhone 7 Plus.

 

[froztheart]

Yes, please refer to earlier report from my side, for StarHub Prepaid S plan (5G), VoWiFi works fine on an old iPhone 7 Plus.

Yeah, saw that.
Weird then since have tested that it should no longer be network issue since all equipment has been replaced, and on stock firmware & settings.
Moreover, tested on 2 different network too.. hmmm.....

 

[xiaofan]

Yeah, saw that.
Weird then since have tested that it should no longer be network issue since all equipment has been replaced, and on stock firmware & settings.
Moreover, tested on 2 different network too.. hmmm.....

Maybe you can also wait for reports from other iPhone users on StarHub network (StarHub, Eight, giga, Cuniq and RedONE).

 

[A7997A]

Data point for future reference.

VoWIFI working on Pixel with ST (MNO) SIM.
VoWIFI working on my iPhones too now.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------

NEW ONT replaced by ISP, replaced NEW ASUS routers, stock firmwares without any changes in settings out of the box.

Do you know which change was the one that made the difference for you ?

Yes, having an existing VPN connection on the phone can impact VoWifi, since a full tunnel VPN sends EVERYTHING through the tunnel, including your VoWifi connection, and you also have to deal with MTU etc.

Okay, tested across my devices and my findings are:

Forcing VoWIFI (Tested on both WIFI network @ residence to ensure not ISP/Router issue)
WIFI Assist - OFF
Airplane Mode - ON
iPhone 16PM (IOS 26.1) - M1 & MY (Roaming on SIMBA) SIM both reflected VoWIFI
iPhone 13PM (IOS 18.7.1) - ST & MR SIM, ONLY ST SIM reflected VoWIFI
iPhone 12P (IOS 18.7.1) - SH & MY SIM (Roaming on Starhub), ONLY MY SIM reflected VoWIFI

Noticed that VoWIFI is lost once Cellular is established back, while secondary SIM's VoWIFI remains (for MY SIM, yet to test out with M1/ST as secondary SIM).

Also, seems like VoWIFI doesn't work on Starhub from the test I conducted across Starhub (MNO), MR & CUniq (MVNOs) since all does not reflect VoWIFI.
Going to check with Starhub for further clarification.

VoWifi for eight works on iPhone XR & 14, I tested just before posting this :
https://forums.hardwarezone.com.sg/threads/singtel-wifi-calling.7121039/page-9#post-157883377

Your MR is 4G or 5G plan ? If 4G plan is M1 and may or may not work with VoWifi.
Does MR VoWifi works on your Pixel (or any Android phone) ?

 

[loganrunning]

Noticed that VoWIFI is lost once Cellular is established back, while secondary SIM's VoWIFI remains (for MY SIM, yet to test out with M1/ST as secondary SIM).

interesting..... dunno if it's phone or telco or some combination of both.
on my android phones, when i turn off airplane mode, i recently noticed (ok, i didn't take note before during the initial phase), that VoWiFi didn't turn on until about 5-10 min later.

it stayed on even with cell connection also on.

Also, seems like VoWIFI doesn't work on Starhub from the test I conducted across Starhub (MNO), MR & CUniq (MVNOs) since all does not reflect VoWIFI.
Going to check with Starhub for further clarification.

one of my phones (1+12) is using eight, on starhub backend. probably the front end is also starhub.

if only the telcos would issue a definitive statement on what is needed, and the conditions it works.
not holding my breath.....

 

[froztheart]

Do you know which change was the one that made the difference for you ?

Yes, having an existing VPN connection on the phone can impact VoWifi, since a full tunnel VPN sends EVERYTHING through the tunnel, including your VoWifi connection, and you also have to deal with MTU etc.

Unfortunately, no. Didn't managed to identify any possible causes.

Only have DDNS setup for my mobile device to connect back to routers when overseas.
No other VPN/network settings configured too.

VoWifi for eight works on iPhone XR & 14, I tested just before posting this :
https://forums.hardwarezone.com.sg/threads/singtel-wifi-calling.7121039/page-9#post-157883377

Your MR is 4G or 5G plan ? If 4G plan is M1 and may or may not work with VoWifi.
Does MR VoWifi works on your Pixel (or any Android phone) ?

Right, so it works on your iPhone too.
Yes, am clear that MR has 2 differnet providers. 5G MR for me so it's under Starhub. Can't test my MR as it's an eSIM.
Tested on my POCO F7 Pro with Starhub (MNO) and there's VoWIFI on both my home networks. Don't seem to a router/network equipment issue.

 

[froztheart]

interesting..... dunno if it's phone or telco or some combination of both.
on my android phones, when i turn off airplane mode, i recently noticed (ok, i didn't take note before during the initial phase), that VoWiFi didn't turn on until about 5-10 min later.

it stayed on even with cell connection also on.

Right, noticed that it takes a while for the VoWIFI to reflect too.
When turning on Airplane mode to force VoWIFI, doesn't seem to reflect for me, no VoWIFI reflected on my Android..

one of my phones (1+12) is using eight, on starhub backend. probably the front end is also starhub.

if only the telcos would issue a definitive statement on what is needed, and the conditions it works.
not holding my breath.....

Yes, unfortunately it's all pretty vague so require us HWZers to test and potentially get some findings that might pinpoint what might be the cause/conditions before VoWIFI will be established.
But even with that, telcos can change anytime so that's that too...

 

[loganrunning]

But even with that, telcos can change anytime so that's that too...

sadly true. just needs a policy change internally, which cascades into (our) real life without notice.
then we are scratching our heads as to why it doesn't work anymore, and we go running around in circles to establish the causes.

telcos - you can't live with them, you can't live without them.