[Galaxy S I9000 Q&A, Help & Troubleshooting] louie604:
I am unfortunately one of those that have this problem as well.

I've had my phone for a few weeks now, first couple weeks went by flawlessly (only thing i noticed is that I would intermittently lose signal, both voice and data, while in my room. It would go from a few bars to no signal). I had my phone rooted and lagfixed within the first week and a few games installed. Running on Bell in Vancouver.

To keep things short and simple, my phone worked great up until last weekend (Oct. 22 - 23). That was when I first noticed that my screen would not turn back on while i had it charging. I held the power button down for ~10secs to restart the phone and noticed that my battery lost about 20% from when i last checked. To me, this meant that the phone was still on but something had locked up the phone and was using 100% of the CPU. Just last night, my phone dropped signal again and a couple minutes later, i went to check it again and it locked up again with the screen off. This to me, backed up the theory that the whole issue is related to data/apn that you guys have discussed here. I read the post about restricting it to the 850 band and I've done just that. So far, it's been just about 14hrs since I did it and haven't had any comas/lockups yet (I'd normally get one or two at around 6am). I've actually also noticed my battery life has improved too (while just leaving the phone to idle/standby while im working). Normally i'd lose about 5-10% after unplugging it from the charger for a few hours... now I've only lost just 1% after 3 hours of idling.

Anyway, I guess what I'm trying to say is that, for what ever the reason may be, the SGS seems to have trouble locking on the the higher bands (1900/2100) and as a result it'll keep falling back to the 850 band but constantly has trouble changing over/handing over (whatever the term is) the connection (meaning the phone loses signal with the towers) and as it tries to reconnect, i can only assume that the phone gets confused and freaks out as while it is falling back and connecting to the 850 band, it notices a better 1900 connection and tries to connect to that too WHILE already trying to connect to the 850 band. As a result, the CPU locks at 100% usage since the APN is most likely screwed up hence the lockup/comas and the phone gets stuck in an endless loop of trying to connect, which also explains why the battery is getting drained even though the screen doesnt turn on anymore.

I may be wrong, but that's just my guess in this whole issue. To me, this is most likely a software issue, hence why Froyo users haven't complained about it. The only thing that puzzles me still is, why did most of our phones work without issues out of the box and only started happening a couple weeks after?..

I don't remember, but has anyone tried locking the phone just at the 1900 band? If someone has and hasn't noticed any comas while using just the 1900 band, then it may just prove my whole idea theory.. I personally stuck with the 850 band as it resulted in me having better signal, but I will probably try locking it to just 1900 tonight as my phone seems to only lock up at home where it constantly drops signal even though i get 3-4 bars -__-

*Edit at 1:56PM PST on Oct 26, 2010*

So I got impatient and restricted it to the WCDMA 1900 band only. Will see how it goes when I get home since I always have signal where I work and never locked up on me while at work.

Will post back as soon as something happens, otherwise I'll post back tomorrow with an update if it's working fine.