1. Go to the dialer and press *#*#4636#*#*
2. Click on "Phone Information"
3. You should notice almost towards the bottom radio settings, Make sure the radio is on and change the settings from WCDMA to GSM (auto)
4. Exit out of the screen by pressing the back button
5. Reset the phone and you will have service.
If your phone keeps reverting to WCDMA follow these directions
1. Use GTG's Ultimate Unbrick here http://forum.xda-developers.com/show....php?t=1116251
2. When you are reverted to stock rom, use Super 1 Click to root. which can be found here http://shortfuse.org/ Restart phone.
3. Follow these instructions to get 3e then clockwork Recovery on your phone here http://forum.xda-developers.com/show....php?t=1107881 PM me if you need Root Explorer APK
4. Boot into recovery. FULL WIPE DATA DALVIK EVERYTHING
5. Flash ICS Rom of your choice. I recommend Paranoid Android which you can find here. http://d-h.st/NMp don't bother with GAPPS for now
6. Boot up android and reboot into recovery FULL WIPE DATA DALVIK EVERYTHING
7. Flash the Jelly Bean ROM of your choice. I recommend Unofficial CM10 8/31 - Butter - MTD which can be found here http://d-h.st/MZ9 Don't bother with Kernel or GAPPS for now
8. If you have a boot loop that's normal, pull out the battery, re flash then reboot into android
9. Once the device is booted, make sure you have a strong signal and can make phone calls. THEN reboot into recovery
10. Flash OC Kernel and GAPPS of your choice. MAKE SURE to use this kernel http://d-h.st/mcN if you used Unofficial CM10 8/31 - Butter - MTD. I recommend Justin's GAPPS which can be found here http://forum.xda-developers.com/show....php?t=1797292
11. Reboot and viola! You should have service for ever and ever.
This no service problem is caused by your IMEI getting wiped when you flash straight from stock to jelly bean.
WARNING I AM NOT RESPONSIBLE IF YOU BRICK YOUR PHONE, THIS IS JUST A GUIDE WHICH HAS WORKED FOR ME AND WISH TO SHARE IN HOPES OF HELPING OTHERS. I DON'T WANT CREDIT OR DONATIONS, HELPING ANOTHER PERSON IS GOOD ENOUGH FOR ME.
Follow me @khalidbalid on twitter if you have any questions, concerns or just want a laugh from time to time.
I hope this helps.