you can get more info on computer forum.

I use ATT gophone. Many on computer forum use PagePlus (on Verizon). Color-Big-Ball-Small uses T-Mobile. Some prepaid have pay-as-you-go plan (my), others have monthly plan.

 

I like an unlocked GSM world phone, so I don't need to switch the phone for travel outside the country. I also want the phone to have bluetooth and wifi. So I can only use prepaid plan from ATT and Tmobile. TMobile is a little cheap.

 

My first choice is unlocked Nokia N-series and E-series (around $200-300). I'm also considering unlocked, non-contract iPhone4s (around $800).