I just added a Net10 sim card to an unlocked iPhone 5 tonight. I activated everything with Net10.
I opened safari and went to Net10's website which has an option "DATA/APN Settings" then selected "AT&T DATA SETTINGS" and then selected "IPHONE" -- this opened up an APN Profile Installer. I clicked install. It installs immediately. I then restarted my phone.
I turned off wireless to check that I had cellular data.
1. I browsed to CNN in safari. Worked.
2. I sent a text. Worked as iMessage.
3. I sent a picture. Does not work.