Not sure which phone you have (going to buy) but almost 99.9% sure it is wifi. Given that fact, you can use it to log onto data sources, email, web etc. I bought the HTC One X and had it for 2 days prior to getting on ST. I managed to get everything set, launcher, apps, screens etc.
As far as porting goes.................i did this yesterday. After trying ST and the phone for 12 days i pulled the trigger. I plan to keep the phone so i ported my regular number. I came from Page Plus and i needed my account number and pin number. All took only about 30 minutes. Should happen quite fast as long as your info is accurate.
I for one am very happy with the service (AT&T sims use the AT&T towers. They are strong in my area) and the phone (love the One X).
If i can be of any help just ask
Oh.........BTW..........data usage is not an issue for 99% of us. There are quite a few threads on here complaining about data but it is my guess the folks are "data hogs". In 13 days i have only used 258mb of data. The phone is "wide open" all the time. I for one at least do 90% of the time use my TV for movies, my stereo for music, and my PC for youtube. LOL