Pantech Matrix C740

My daughter=s C740 continually resets - sometimes every few minutes, sometimes a few times a day. We are on AT@T. When it happens, we get the AT@T splash screen, green 'loading' bar, then the phone works fine.

AT@T support pushed a software update/reset a few days ago from their help desk. No better now. I've reset the phone per the user manual to no avail.

Any suggestions?