IF YOU AQRE GETTING ERROR MESSAGE == "mobile network not available"
Ok here is steps again for you.
1. i downloadeD orignal samsung firmware of my country from www.samfirmware.com
2. Then i flashed it via odin.
3.then i rooted my phone. you can see old post about how to root. thats easy.
4. then i went to my samsung custumer service center. he was my friend. just switch your mobile On n connect it to there pc. he opened a software named SAMSUNG 3G TOOL. n there i see option REPAIR IMEI. he just clicked in it. then i typed my orignal Imei and pressed Ok.
And it done in 10 seconds.. n phone got restarted automatic.
I seen my imei changed n got my network back . i was happy.
cynogenmod 7 & cynogenmod 9 both are crap for samsung galaxy s2.
Because there is no android market and network on/off instaly.. u cannot make call if u install that. so beter use orignal samsung firmware in s2.
Hope this msg help you. gud luck.