I changed from iPhone 5s to iPhone 8 Plus recently. I upgraded my plans from First Gold to FIRST Gold Plus. With my older phone and older plan everything worked just fine until I changed my phone and plan under Device Bundle Plan.
However, I tried to input my number in my Apple ID so that i can receive a verification code but the code has never sent to my number.
I tried to activate my imessage and facetime but once i click on the button, I received bunch of weird message "????y???REG-RESP?V=3;r=1219516422;N.....: However, this has stopped when i went to lodge a report to celcom.
BUT STILL NO VERIFICATION CODE RECIEVED AND IMESSAGE ACTIVATION STILL UNSUCCESSFUL.
MY NUMBER STILL HAS NOT SHOWN IN THE IMESSAGE AND FACETIME.
Are u still having issues with the imessage thing? There's a post in LowYat that probably has a solution.
You can check it out here. Or there's also troubleshooting steps from Apple, here.