Hi Everyone, its my first post and Im glad to contribute- I updated my jailbraked unlocked iphone from 1.1.4 to 2.1 with quikpwn for windows. WOrked excellent for some weeks until sudden signal loss to couple bars to NO Service... Started reading posts and tried re-programing firware 2.1, reboot several times and changed SIM. No fix. updated to 2.2, worked for couple hours and NO service again. Finally, someone posted about changing belt case and I did try. The damn magnet in the lid was affecting my comm board or something else...
So get rid of the magnet lid cases and did the next procedure

airplane mode-- remove sim --- ok to no sim card messages then turn airplane mode off and replace sim.

ISSUE FIXED.. Now I have been carrying my iphone on my pocket for 24 hrs and excellent signal and even higher level than before.. stayed on firmware 2.2.... GREAT THANK YOU ALL...

-DJ