I have the 9.99 t-mo web2go plan and these are my settings:

Cellular Data
APN internet2.voicestream.com

everything else is blank

MMS
APN wap.tmobile.com
username and password are blank
mmsc http://216.155.174.84/servlets/mms
mms proxy 216.155.165.50:8080

and the rest blank... I dont have anything downloaded off cydia and legacy doesn't show up when I search for it. Any help would be greatly appreciated. also im running an Iphone 3g 3.1.2

thanks!