Well, i don't think that you'll get AT&T firmware back on your phone.
Untill now we know that W580 and K800 are upgraded to CID53 by SEUS.
Be careful
LE: I found a list with all the phones that are supposed to pe upgraded to CID53
- K530c
- K550i
- K550iM
- K610i
- K618i
- K770i
- K790i
- K800i
- K810i
- K818c
- S500i
- T650i
- T658c
- V630i
- W580i
- W610i
- W660i
- W710i
- W830i
- W850i
- W880i
- W888c
- Z610i
- Z710i