Google Makes Voice Number Porting Available to All
Google today announced that all users of Google Voice will be able to port their existing wireless number from their carrier to Google Voice. The process costs $20 and takes about 24 hours to complete. Google reminds Google Voice users interested in porting their number that doing so will cancel their existing wireless contract, which may leave users responsible for early termination fees. Number porting will be available to new users in a few weeks.
While policies can vary, generally it's like pulling teeth getting smaller prepaid carriers to release your number quickly, and with some (Tracfone) it's almost not even worth it.
This way, you use your Google Voice number, so if you decide to switch carriers, you don't have to worry about porting, you just change stuff from google's website.
And if you have a smartphone, this basically means you have unlimited SMS (no MMS yet), which can save you up to $20 a month.
Is it possible - AT&T
And for what its worth, my contact extension was done in December at Best Buy, mainly because the local AT&T agent was out of stock.