Thumbs down 3g data connection make reboot

Hello everyone, I have a problem I dont know how to solve it, I got a Milestone 2 on Movistar Argentina, originally locked to Personal, The phone works perfect without a sim card, or in 2g mode, not a single reboot, I can make calls, send messages, use all the apps, but when I turn on data connection, the phone reboots itself, I don't know what to do.
Hope some one can help me.
Thank you.