Originally Posted by bruce081
I just did this new at all this. and put it on a 19020a. now the phone powers up fine and on gingerbread. but i have no cell service... HELP PLEASE. How do I change it to a i9020a version to fix my phone? Or am I screwed? When I did it i took a backup so i have that image on my phone. but when I try to use that it tells me MD5 mismatched
You flashed the wrong firmware with the wrong radio, that's why you have no cell service.
If you haven't fix it yet, you need to flash a full i9020a firmware rom onto your phone via clockworkmod. See this thread on XDA for the firmware version you need (2.3.6 is the latest):
[I9020A][REF] All OTA and Available Full ROM Packages - xda-developers
Once you have the firmwave downloaded, rename it to "update.zip" and copy it to your Nexus S phone. Reboot into recovery, wipe data and cache, then go to advanced and wipe dalvik cache - this dalvik cache wipe is VERY important and must be done to wipe any remnants of the other OS version. Go back and run the update.zip file, wait for it to complete (~5 mins), reboot from recovery.
You should now have gingerbread v2.3.6 installed and ready to setup.