My Atrix has started to reboot constantly. Tried everything (I mean everything) abd finally had ATT replace it. The replacement had the same problem right out of the box. When I was troubleshooting the original phone I ran it without a sim and it still rebooted every few minutes. Okay here is where it gets weird... I have an old Nokia flip Go-phone for work. I switched sim cards with the Atrix and both phones are working fine. The Atrix hasn't rebooted in several hours. As an experiment I pulled the go-phone sim out of the Atrix and ran the Atrix with its own sim & then without a sim. It rebooted constantly. Put the go-phone sim back in and it is fine. If the Atrix sim was the problem wouldn't it mess up the go-phone? And if the Atrix sim was the problem wouldn't the Atrix run fine without a sim? WTH?