its so easy if the phone effs haven't corrupt
if corrupted then write the correct nv with z3x 3g tool.
bro 1st update your phone to 2.3.5 the then root your mobile on the unlock root as link below
Unlock Root of Android
download it and install it then root your galaxy or any android phone easily then goto repair task or change the imei of your phone easily with z3x
with z3x
1.open z3x version 12.4
2.select model i9100
3.power on phone
4.Enable debugging on: menu>application settings>development
5.connect cable and install driver..
6.then press repair
7.then enter the serial number on which written on phone battery side or your desire
imei only check s.number.
8.click repair.
9.wait till finish...
Count supported models - 309
Android Version: 2.3.5
Model: GT-I9100
Product Code: GT-I9100RWAKOR
Phone Version: I9100XXKI3
PDA Version: I9100XXKI3
CSC Version: I9100OXAKI3
IMEI: 004999010640000
Checking ROOT... true
Rooting Phones, Please Wait... OK
Checking ROOT... TRUE
Reading Data From Phone... OK
Writing NV Data To Phone... OK
Rebooting Phone... OK
Searching Samsung USB Modem... Detected COM34
Bypass MSL... read done (1)
Phone Found Samsung USB Modem... Detected COM34
new imei is 355995457852474
repair imei done...
Done with Samsung Tool ver 12.4
try then post.
by asadzai br.