2 possibilities...no1 is sim slot, try just giving it a really good clean of the 6 contact pins, make sure the bottom spring on that tray is moving to let the phone know the sim card is inserted.

no.2 damage to the "wing" near connector 7. it's got the antenna wiring so if too much force trying to get board out of frame then this gets damaged.

It may be the battery, old 3gs batteries wont work right on newest iOS .

May try downgrade to iOS 4.1 (this is the only firware than can be downgraded whit a custom firmware) to see if the ICCID error fixes or try whit a newer battery part number like APN 616-0428.

Hope it helps.

Luis

i have the same problem but after opening the phone and change the wifi antenna only, so its definately a hardware issue. Everything else is the same so it's not the battery. i have opened/closed the phone many times so i would say its maybe connector 7, i may damaged it and thats will be my next step.

i also noticed that if i close the phone without placing the 7 screws on the motherboard (so the motherboard is not too tied to the back) i may have 1 or 2 bars. in may occasion i have the "searching" up left in the screen but i can send sms and internet browsing but no calls!

hope i helped a bit

I had this problem with a 3g. I installed a really old firmware as the new firmware "upgraded" the baseband. this caused problems with the baseband/connectivity for some reason.

I then installed the latest firmware whilst maintaining the older baseband.

though, as i said this was with a 3G and not a 3Gs.

I had my iPhone imei unlocked now its stuck on no service i don't know hot to fix it please help