I successfully ported my number from AT&T land line to Google Voice using a T-Mobile prepaid SIM card in just a few days without any major problems. DAY 1 (Wednesday) evening:
Started the transfer to T-Mobile at the time of activation of the prepaid T-Mobile SIM card (bypassing
the temporary number). I used my existing
(subsidized, on a non-expired contract) phone, so for the next several days I was swapping between my "main" and this "prepaid" SIM cards.DAY 3 (Friday) evening:
Got a text message on T-Mobile "Your number has been transferred". But T-Mobile handset doesn't ring yet on incoming calls. Google says can't port from my provider. A check at https://www.wirelessamberalerts.org/index.jsp
shows the number is NOT a T-Mobile one yet.DAY 4 (Saturday) morning:
T-mobile phone rings on incoming calls. A check at https://www.wirelessamberalerts.org/index.jsp
shows the number is recognized as a T-Mobile one. Google says OK to port.
Before continuing, I followed these steps to create a PIN for my T-Mobile account.
1. Use your phone to call 611.
2. Say manage my account.
3. Create bill account PIN.
4. Enter 4 digit for your PIN. (I inputted the same PIN that I created at the SIM activation time).
5. Verify your PIN.
Immediately started porting to a fresh new Google voice account. GV never asked me about my T-Mobile PIN or last 4 SSN.
Immediately received an email "Oops! Issue with your Google Voice Number Porting Request", GV says "Error Code: Password/PIN required or incorrect(Prepaid PIN required)". I enter my T-Mobile PIN and my REAL
last 4 SSN (did NOT input the T-Mobile PIN in both fields).DAY 5 (Sunday) morning:
I received an email to say the number porting was complete and everything is working as expected.
Overall, the process was straightforward and the information that I found in this forum was a great help.