it work on ATT phone on China Unicom
Tried this yesterday, after spending 8 months in China frustrated with an AT&T locked iPhone 4, OS 5.1 and BB 4.12.01.
Used iTunes 10.6.1(7) - latest version as of 4/23/2012 - jailbroke with redSn0w, but this is a tethered jailbreak because of OS 5.1 (people on early OS may be OK with untethered) meaning I have to reboot connected to the computer after a hard reset, and installed cydia as part of redS0w. Downloaded SAM (got error msgs on the download but it worked), tried a couple of times spoofing as per the directions, before it finally worked (i think your SAM and SIM numbers need to be the same).
iTunes never properly said it was activated, but just showed a normal screen when the phone was connected (with the iPhone4 icon and name on the right side), and didn't show the message "your phone can not be activated because it doesn't have a proper SIM in it".
Finally after 3 hrs of download, reading, button pushing, the bars showing signal on China Unicom appeared!!
You need the NEW SIM card to get this to work, you do not need your old AT&T SIM. I already had my AT&T iPhone4 synce to this computer before, so I'm not sure if a brand new unsynced iPhone will work with this hack.
iMessage works, and so does 3G, so I'm pretty happy - especially since it is free.
Best of luck everyone, -I think it is interesting the original hack came from a Chinese netizen- times are a changing, as I can see in the P.R. China.
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There is a jailbreak for 5.1 on iPhone 4, you just need to be tethered still, try redsn0w.
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Keep trying, it didn't work about 10 times, and then I got it to finally work. Dunno why, the server was up when I checked in the browser, not sure if it'll remain this way.
is there other way to add (repo.bingner.com) to cydia I been try to do that for a week now I keep get a message "verification error"