If you port your number without changing it with t-mobile first, you'll be canceling your service (it's the same as porting your number to Verizon or Sprint). You'll need to get a new number with them first.
Be aware if you do this, you'll need to use the Google Voice app to text (or the recipient will see your real number, which they may not recognize). You will also need a data connection to initiate a call using Google Voice (again, or they'll see your real number).
I have a post around here somewhere explaining it in more detail because I went through this (porting the number I've used for years to Google Voice from Verizon) and had to switch back due to what I saw as drawbacks. I'll try to dig it out when I'm in front of a pc.
I still use Voice for voicemail though, and as a number I give out to people I don't want having my real number (it's easier to block them). Was just too hard to make the switch with a number that everyone I know has.
Posted via Android Central App