LB1120 connects/disconnects

I've a brand new LB1120. I've tried SIMs from ATT, and 2x from T-Mobile, but the connection won't stay up. It connects, gives me all green lights (with 3 out of 4 bars signal), but then 20 seconds later it disconnects and cycles around again. 

It doesn't stay up long enough to download the latest firmware and I've tried factory resetting it. 

Any ideas? Or should I return and assume it's a hardware problem?