Is it correct Sms and voice calls between 2 simba lines while overseas will be consider free and does not deplete the monthly allowance??
Don't think sending SMS works, not sure why you want to do that, why not whatsapp/telegram/signal ?
Voice call between 2 Simba lines should be free : Caller is free outgoing to SG Mobile. Receiver is Free Roaming.
I wonder about outgoing calls to local numbers of destination though, free IDD minutes doesn't include Taiwan, but I recall making call to local Taiwan numbers with no wallet balance nor IDD pack.
See
https://support.simba.sg/hc/en-us/articles/4487047558681-Does-roaming-cover-calls-and-SMS :
Does roaming cover calls and SMS?
Besides data roaming, SIMBA subscribers can enjoy calls to and from Singapore without any roaming charges.
You won’t longer need to reject incoming calls when you are travelling abroad with SIMBA.
Voice Calls
1. Calls to and from Singapore do not have additional roaming charges.
2. Outgoing calls to any Singapore mobile number is free, while outgoing calls to a Singapore fixed line will be deducted from the plan’s Local Fixed Line Minutes allowance (Please add +65 if you are making calls to Singapore while roaming)
3. Outgoing calls to local numbers of the destination you visit is supported. You can either purchase a
SIMBA Super IDD Pack or deduct from SIMBA Wallet based on prevailing
IDD rates.
SMS
Incoming SMSs are free. Outgoing SMSs are not supported while roaming.