Family Map cannot locate HTC Desire

My son's phone died and I bought him an HTC Desire and a new sim card. Family map worked ok before, but now, with the new phone, will not locate unless he is talking on the phone. When he is talking on the phone it finds it just fine. If not, family map returns the message saying his phone is off or out of AT&T coverage.

I've worked with his phone myself. With his phone on, and good signal, it will not locate the phone unless it is being talked on. I deleted the number from the family map account and then re-added. Also I clicked the text which allows the phone to be tracked.