Default MMS


I have a question about MMS. To send my mms I must turn on manually my data and I can't receive any mms if my data is off. I have this issue with all ROMs except SlimBeam. On Slimbean,no need to turn on manually the data, it's automatic.

Someone is able to explain me..why ? Why Slimbean is so special ROM ? I can't solve this issue and I can't understand baucause the APN settings are the same on all ROM.

Device : Samsung Galaxy Nexus
ROM: Purity 4.3
Kernel : FK