Wirelessly posted (BB 8900: BlackBerry8900/4.6.1.250 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/301)
Do a software unlock, and it should work fine. Keep in mind you get no minutes with the $1/day prepaid plan. As far as getting internet working, these are tmobiles apn's, usually the sidekick apn or g1 apn will work with the prepaid sim:
Access Points Names (APNs)
T-Mobile Internet: Internet2.voicestream.com
T-Mobile Internet VPN: Internet3.voicestream.com
Web2Go/t-zones: wap.voicestream.com
BlackBerry: blackberry.net
Sidekick: hiptop.t-mobile.com
T-Mobile G1: epc.t-mobile.com