Here is solution for USC N2 where after upgrading modem to MB1, data breaks.
Though this is not perfect solution, this does make DATA available on N2. One has to repeat this process every reboot.
So I believe same must be applicable and good for S3.
You are editing NV items so be careful. Don't do if you do not know what you are doing.
Downgrade Radio from MB1 to LL1
Edit NV item 896 From 1 to 0
THis NV item is UIM_FIRST_INSTRUCTION_CLASS
0 is GSM (PHone will not read UICC ID)
1 is UMTS (Phone will read UICC ID but Data will not work)
2 is UICC
3 is UICC with other suffixes.
Then follow this
http://www.rimweb.in/forums/topic/35979-samsung-galaxy-s3/page-36#entry292974
OR
http://www.rimweb.in/forums/topic/35979-samsung-galaxy-s3/page-36#entry292998