Same problem here
Same problem here. 32GB 3GS iphone, 3.1.2, baseband 05.11.07, iBoot 6.02
Did the 3.1.2 update from windows, ran blackra1n RC3, jailbroke it,
then installed cydia & sn0w from the iphone blackra1n app.
SIM is from Vodafone ES (Spain). For like a couple hours I was able to
make and receive a couple phone calls (though I noticed carrier signal
fluctuated a lot), I set up mobile network parameters and sent &
received MMS, used 3G data connection, etc.
However people complained they cannot hear me clearly, in standby I
got several "you got disconnected from the network", then it
completely lost carrier signal and shown "no service". I tried
reseting network settings, turn airplane mode on and off, to no avail.
Tried running snow again, to no avail; now it doesnt even get signal.
Tried updating to 3.1.2 again, and repeat the process, the same, no service.
Tried updating w/ a mac, same process on it, no service.
The same SIM on a iphone 2G updated to 3.1.2, jailbroken with
blackra1n RC3 and then neutered, on the same windows computer has full
signal and works like a charm.
I restored the 3GS by manually downloading the firmware file iphone2,1_3.1.2_7d11_restore.ipsw and using shift-restore to explicitly select it, as I noticed the file iTunes had downloaded was iphone1,2_3.1.2_7d11_restore.ipsw.
Signal is also very weak now, but it barely gets carrier, though signal is always -90 or higher.
Don't know if iTunes just keeps the latest downloaded file; I first upgraded the 3GS, then the 2G, maybe that's why the file I found was iphone1,2_3.1.2_7d11_restore.ipsw instead...
Googled for hours to no avail.