My last 2 responses were in reply to questions about tethering and CommCenter from 2 different posters.
Blackra1n does seem to cause/aggravate the wifi problem.
Yeah, I had a problem with wifi on blackra1n too on my 3GS. I googled it and found instructions to reset the network settings. This caused the phone to not boot back up and had to be restored. After that and blackra1ning again, I've had no Wifi issues in months, even with restoring from my old backup.
BUT (and there is a BUT)...
...I've been having this service dropout crap for the past few months and it's taking a lot of strength to NOT punch the phone when it happens (it get's that bad). Everytime I make a call or someone calls me after the phone has sat idle for a period of time, the call just completely drops out after about 2 minutes on the call. EVERYTIME. Second call attempt, once it finally connects back to service, the call is fine until I hang up. At my house, I can't use 3G almost at all, EVEN WITH 5 bars. Sometimes it won't even send texts or MMS and I have to switch to Edge so I don't keep getting "Message Send Failure" everytime. House is the phone nonfunctional on 3G even with 5 bars??? Also, I have my music studio detached from my house. I come in the house to get a drink and my wife's like "why didn't you answer your phone? I called you like 5 times!" And the whole time, my phone never even rang. Also, a lot of times, on 3G, the phone will go to No Service after sending a successful MMS.
It's just getting really frustrating. It happens on my wifes 3G as well, which is jailbroken on 3.1.2 like my 3GS. Also, let me mention that both of us are NOT USING BLACKSNOW. But we are having the same issues everyone is mentioning here. I don't know if it's Blackra1n related, but I don't think it's Blacksnow related since we don't have it, even though some of you say it's "confirmed" to be Blacksnow. And again, this issue is not to be confused with the Wifi issue. Like I said, I solved that with a restore/rejailbreak. And I also don't have PushFix on my phone, if that even has anything to do with it.
So before I decide to dump AT&T, I've decided to run stock for a couple of days to see how it is. I have an original release 3GS (from the day it released last July) and have been jailbroken since that first day. I just restored to stock 3.1.2 a few hours ago and so far, so good at my house; even on 3G. MMS is sending right away, whereas it would take 10-15 seconds with blackra1n. Service hasn't dropped out yet. If it still does it, I think I might move on to a Droid or something. I don't want to. I hate to give up the iPhone. It's that phone you get and wonder why you didn't have it sooner. And the Droid seems like the closest thing to an iPhone out there (I hate BB). But I can't deal with this any longer. So the test is on; "AT&T or Blackra1n, who's causing the problem?" We'll see!