Use T-Mobile,
not one of those other two. Reason: the small re-sellers have very little expertise in number porting, and are the #2 cause of failed ports (the #1 cause is the user entering incorrect information).
Yes, you need the mobile phone to be fully working, including making and receiving voice phone calls and SMS, before you start the port into Google Voice. So, add some call credits.
This is documented here:
http://www.obihai.com/porttutorial