Hopefully I can help...
Like you guys, I was on Sprint and integrated with Google Voice. I was using a Galaxy Nexus...if that matters at all. I knew I wanted to leave and head over to T-Mobile prepaid so this is what I did...
- disabled my google voice integration so I could check to see if my number was eligible to port. i figured it would be, but just wanted to make sure...
https://www.google.com/voice/porting
- after it was ok, I went ahead and reintegrated it while I waited for my Nexus 4. everything went back to the way it was before and worked perfectly.
- got tired of waiting for my nexus 4 and purchased a htc one s (tmo branded).
- purchased a micro sim online for 99 cents.
- activated it online and got a new number from t-mobile
- set up the one s with google voice and had the new number point to my old number. everything worked as it should...people called my old number and my new phone would ring. nobody new i had a new number because it was so well integrated into the gvoice app.
- decided that this worked well enough and finally decided to port out of sprint and into google voice.
- disintegrated and went right ahead and kicked off the port process. it was simple and painless...a bunch of boxes to check to make sure you are good with everything. it took exactly 24 hours for my sprint phone to stop working and my contract to be terminated. text messages took another 36 hours to fully work. they warn you that it may take up to 3 business days.
- so now i'm using my one s and google voice...away from sprint completely. I love it!
- just patiently waiting for my nexus 4 to come...out for delivery on the big brown truck...
Hope that helps and feel free to ask more questions...I'm sure I wasn't clear or can add more detail.
Thanks,
Doug