Default [Noob extravaganza] some questions.

I have a galaxy s3 and use mostly asop ROMs but some of the ones that I would really like to use do not have working mobile data for me. This s3 is the s968c, which is the straight talk model. However, Verizon ROMs(aosp) and recoveries(cwm,philz) can be flashed to the phone with no problem. Well, not all ROMs.. Working ROMs include CM, AOKP and Slim but when I try and flash, say.. Gummy,LS or Carbon I have no mobile data.. As a noob, am I over looking some easy mod that would fix this issue. I'm just stumped as why some work and others don't. Thanks in advance.