Just a quick update, I think the phone is fixed now. What I did was use SP Flash Tool to flash back to the stock ICS, then I rooted and installed TWRP and factory reset/wiped/formatted everything in sight! Then flashed the custom JB ROM I like and there you go.. happy days it's rock solid. Another bonus is that odd little pre-recovery menu has gone so I can get straight into TWRP. I'll update the thread if anything changes but I'm confident it's fixed. Now for the bad news.... I was so convinced I had a bad phone I ordered a G3 Plus and it should arrive tomorrow or the day after, oh well it looks like a decent little upgrade and I'll sell my G3N easily as it's obviously like new.
I think I have the same issue.
I have a Factory G3 , not rooted, no modifications, never flashed,
you are the first i saw with the same problem - I am actually still in the analysis phase :-( . After prolonged standbytimes (on or off power) i cannot be called any more and cannot make calls outgoing. I can't SMS or receive SMS , not GSM Internet connectivity. WIFI Works great at those times, Whatsapp and other data apps work over WIFI, but all GSM Services are dead.
The phone sais i have Connection (H data) and full bar's on GSM signal. It just seems to have forgotten to logon to the cell tower. (Not sure if switching cell towers has anything to do with it)
I tried Airplane mode in the Menu bar (Swipe down) and back on regular mode - Still no connection reset.
I had this happen in the middle of a phone call (while in the car) moving from one tower to the next and not beeing able to call back - no connection.
Today i found out that using teh settings menu - MORE - Select airplane mode in Settings - it deactivates ,Back one menu (more) and down again to deselect Airplane - it actually reconnects correctly and resets connection to be able to call.
There seems to be adifference between airplane mode from the Shortcut menu (swipe down) and the actual Settings menu.
I would love to get rid of the problem too, but I have never reset my phone.
I would like to avoid rooting the phone since TV apps in Holland with my provider don't work on rooted androids.
If you can point me to a more detailed instruction (keeping current data and setting) to do what you did , i would be greatfull (pretend i don't know what i'm doing :-) since i dont )