I use the Witopia VPN service on both my iPad and my Nexus 4.
iPad+ WiFi = VPN works
iPad + 4G = VPN works (the 4G is native AT&T)
Android + WiFi = VPN works
Android + 4G = doesn't work (the 4G is AT&T via Net10)
I've worked with Witopia support (they're very good) and their only conclusion is a problem either with AT&T or Net10. Since my iPad+VPN works great with native AT&T my suspicion is Net10 but it could be the non-native AT&T.
Anyone else using a VPN plus AT&T Net10? Any secrets to share?
They might not like the double security. You can be anonymous with Net10 plus the VPN makes everything encrypted. AT&T might not allow this from certain of their own customers, either. Maybe it's a national security thing. Or maybe I'm completely wrong.