No service = downgrade?

[BMNB1tches]

Hi guys, so last week i decided to upgrade from 4.0.1 (jailbroken via jailbreakme.com) to 4.2.1 (and jailbroke with redsn0w) a little later that day i couldnt send messages unless i had 4 or more bars and sometimes 3. Also couldnt make calls unless i have 5 bars, and the call quality is horrible. Also when i turn edge or 3G on i get searching..., then NO SERVICE. I then downgraded back to 4.0.1 and i still have the problem. I dont know what the previous baseband was but the one currently is 5.15.04. Ive been searching google and forums all week and came up with that my baseband is corrupted. What should i do to fix my problem?

Notes
-I do not have a data plan on the iphone
--Please refrain from giving me answers that suggest that i need a data plan for an iphone to work because ive been using it for over a year fine
-if it is the baseband is it possible to downgrade to the lower one or upgrade to the ipad one to fix the problem?

[BMNB1tches]

added data plan today... wasnt the problem

[Cid6.7]

Same thing happens with mine one second I have full bars then drops to searching for signal without moving or doing anything..

Dunno but it all started after I upgraded to the latest baseband..

[shitake83]

the exact same problem here.
ive created a custom firmware with snowbreeze 2.1.2 installed it, tried redsn0w after.

ive tried redsn0w only, with ultrasn0w.nothing.

im starting to lose my faith.
x98car come help us

[BMNB1tches]

ive cut my losses and bought an iphone 4..... lol i hope you find a solution to your problem