I have extensive experience using eSIMs on my iPhone. Here's my experience and guide for porting into giga on eSIM.
1) Sign up to port-in using giga app.
2) The app will say that you are issued a temporary number and you will receive an email with the eSIM QR code, with instructions to install the eSIM immediately. DO NOT do that.
(explanatory note: Usually once you've issued a physical or eSIM with temp number, you can start using it immediately. However, that's not the case with giga. If you install the eSIM immediately, the iPhone installation process will be fine, but the app will tell you that it wasn't installed correctly and ask you to try again, leading to an endless cycle.)
3) Wait for the next email from giga (a day later) telling you the porting-in process has started and will take 1 to 3 days.
4) The porting-in process usually happens close to midnight, you may receive a message from your existing Telco informing you that your line has been cancelled. Your old SIM will stop working and you have no more signal on your phone. But don't be tempted to install the new eSIM yet.
5) Wait for the final email from giga, which says the port-in process was successful.
6) Go ahead to follow the instructions to install the giga eSIM.
7) Giga's eSIM doesn't seem to have a number attached to it. You'll have to key it in yourself and also give a custom name for your eSIM so you can identify it.
(At this stage, the eSIM installation is complete (the phone will tell you it's been activated) and usually you can start using it immediately. But for giga, there's the added step of going into the app itself to press the "activate" button before your mobile line will work.)
8) Extra steps for iMessage / Facetime. Remove your old line and turn off iMessage/Facetime. Restart your phone. Turn on iMessage / Facetime and choose your new line. The activation will not be immediate. You will notice the SMS quota being used in your giga app. That's part of the verification process by Apple. Wait at least a day.
9) Starhub and M1 share the 5G network and based on my experience, it's not as extensive as Singtel's. You will most likely not immediately see the 5G icon on your phone. Toggle the appropriate "5G auto or 5G on" options on your phone and let it switch to 5G when detected.
