[Galaxy S II Q&A, Help & Troubleshooting] fortenbt:
First of all, I'm in the US. I bought the Samsung Galaxy S II GT-I9100 (I'm in the right forum, yes?) off of ebay.

From what I remember, when I received it, it had some weird ROM that I had never heard of and can't remember the name of, along with clockworkmod recovery already installed.

I put cyanogenmod 9.1.0 on it via: [cyanogenmod's site, model galaxys2 cm9.1.0] (I can't post links yet, so I had to remove all of them).

I was using it mainly for development for a while, so I never tried to activate it on a network using a sim card, but recently I tried to do that with StraightTalk (using an AT&T sim). Nothing happened. I rebooted my phone multiple times, took the battery out, reseated the sim card multiple times, etc. Nothing is any different than before I put the sim card in (except the messages about "No sim card installed" have gone away). And in the settings, it shows that it can read the phone number from the sim. I actually talked to their support for a while and they couldn't figure out what was wrong. I tried the sim in 2 other phones and it works fine on those.

I thought maybe the problem was cyanogenmod 9, so I tried installing cyanogenmod 10 nightlies made specifically for this model from: [cyanogen's site, model i9100 cm 10 nightlies] . Same thing with that. No network connection, emergency call only, etc. I've gone through the settings, trying to change things throughout. I've tried to force-connect to AT&T's network via the Mobile network settings -> Network operators menu, but it just says it can't connect to that network. When I tried to connect to TMobile's network, it said this sim card did not allow a connection to that network.

I wanted to double check to make sure the sim was actually unlocked, but none of the magic codes ( [cduu wordpress galaxy s2 secret codes] ) work except to display the IMEI. I've checked a couple online databases to make sure my IMEI is not blacklisted, and both said it was not blacklisted.

Getting pretty much nowhere, I wanted to return it to stock, but when I read up on it, I could not figure out what to do in order to do that. I'm not very experienced with the GS II; my personal phone is the galaxy nexus. After reading up on it, there's about 100 different versions of "stock" for this phone, depending upon what country/language. I don't know where this phone is from, but the only booklet it came with was in French.

I did find the sammobile released firmware versions for jelly bean and ice cream sandwich (I9100XXLSJ_I9100OXXLS1_OXX.zip and I9100XXLPH.zip) from [sammobile's site] . I don't even know if these are technically stock though. The only one I tried to flash was the ice cream sandwich one; the jelly bean one is still downloading. When I tried to flash the ice cream sandwich one using Odin3 v1.85, it just failed. Didn't harm any of the software that was on there, so I'm guessing it found that it wasn't the right version for my hardware?

So after all this work, I'm coming up empty.

Is there anything else I can do to try to troubleshoot why I have no cell network connection at all?

Should I try to flash back to stock and if so, can anyone tell me what english-language version of firmware/software I have to flash/install to my phone to get it back to stock?

Can I provide any more information to help?

Thanks for the time.