4s drops bluetooth connection

My iPhone 4s drops the bluetooth connection from my 2012 Kia. It connects just fine, but after some undetermined period of time the phone seems to forget it is connected. The car still shows it as paired and connected, but calls that come it only get as far as the phone and don't ring through to the car. The phone still seems to know it is connected because the incoming call does not cause the phone to ring. Outgoing calls initiated through the car's handsfree interface start and the phone lights up like it knows it's supposed to do something, but the car then displays a message saying that there is no device connected.

I have deleted and re-paired the phone from the car to no avail. I restored the phone to the original settings to no avail.

The Kia dealer has checked out the bluethooth device in the car and can not find any problems. One of the Kia service technicians said that he had a similar problem when he had an iPhone 4s. He now has a Samsung Galaxy and has not had any problems with bluetooth in the car since switching phones.

The iPhone 4 that my husband uses in the car does not have this problem, so I really don't think that the car is the problem.

Do I have a bad phone? Is this a software issue that can be fixed?