A:Answeryes. i personally know two friends that have done just that. they use their phone on their current wireless plan. you don't have to use it for prepaid.
A:AnswerI am not sure, but I use it with a cheap pay-as-you-go plan. You should be aware that you might need a higher-level plan to have data. The AT&T website should have a good explanation of available plans.
A:AnswerI was able to keep my number when I switched to this phone from a LG Phoenix. Make sure you enter your number at the store when you're setting it up and then test it.