hi. don't sure how i fix this everytime i had this issue but a few days ago i encountered it again. took me some hours, done flashing to stock to restoring and so forth but still it was no good, still no signal because of unknown imei and baseband. then i re-read some things about this issue. finally it lighted up my mind and solved this.
- The Definitive Noobs Guide to Flashing and/or Fixing the SGS4G! POST QUESTIONS HERE! by Juls317 said that Modem ([Mo]dulator [Dem]odulator) -> helps your phone interpret wireless signals sent from your cell network and wireless routers and also send data back to them (flashing different modems can help improve your cell reception) (thanks FB) . once i re-read this , i assumed that this is what i need to bring back my lost imei. (credits to him)
tried flashing a modem of galaxy s 4g and boom! the signal,imei and baseband of my phone came back.
so here's what I did:
I flashed a stock rom of galaxy s 4g. froyo or gb, doesn't matter which two. (via odin) check the pda then reboot
next, I flashed again via odin a bootloader with cwm. (check the bootloader and let it reboot)
then, flashed again via odin a modem of galaxy s 4g (i used kj6 cause i remember mine is kj6) check the phone then reboot
- here's the link of modems by fbis251 (credits to him also)
the reason i flashed a bootloader with cwm is that i have a zip of sgs4g rom in my sd card which i'm using currently.
then i reboot into cwm and flashed my saved rom in sd card via install zip from sd card.
after that, i restored my backup in cwm and there my phone is, still good as my last backup.
i'm not familiar with using the adb terminal emulator so i don't know about those things they said about the efs folder in renaming the .bin files to recover the imei. sorry for not giving the whole step-by-step flashing things but i'm sure you'll understand some things i said especially those who uses Odin. hope this helps!good luck!