Well i fixed it with a modified framework.jar and SEC_MMS.apk (the built-in messaging app). Dont know if someone has modified S2 app and framework for unlimited SMS, have you tried a custom Rom like MIUI or Cyanogen? If there is no modified app/framework on the net then you will have to use GoSMSpro.
This ROM has a different messaging APK so maybe it doesnt have a limit:
GingerMOD:
http://forum.xda-developers.com/showthread.php?t=1220283
And if it doesnt have a limit then these ones also might not have any limit (as they use AOSP apps):
Cyanogen:
http://forum.xda-developers.com/showthread.php?t=1410400
Insanity II:
http://forum.xda-developers.com/showthread.php?t=1170249
Full list of custom roms on XDA:
http://forum.xda-developers.com/showthread.php?t=1253665
Cant find the changelog of MIUI but you can download it here:
http://files.miuiandroid.com/2.4.27/miuiandroid_SGS2-2.4.27.zip