Inadvertent hangups

[hmil3]

I have a Droid X and have had very few problems; however, my wife has an annoying problem with hers. After she talks for 6 minutes or so, even with a strong signal and full battery, she hears a "beep" and the phone hangs up. I watched her while she moved the phone to and from her ear to see if the screen appeared while near her ear, but it didn't, so she shouldn't have been able to accidentally hit the "end" button. Is anyone else having this type of problem.