Hi guys, just wanted to add something to this discussion. GPRS charges are mobile data, not phone calls or text messages. Radiant is an Android smartphone and there are just too many things that can use data to try to guess, but that's where you'll want to look.
If you never use mobile data on your phone, it can be blocked through customer care.
Please let me know if you have any other questions.
Thanks,
Dmitriy