No sound output using the supplied 2.5mm headset adapter on the Sprint Mogul

[atlas1]

When I try to use the supplied Sprint Mogul headset adapter I get no sound output. If I use the headset directly plugged in w/o the adapter it works fine. I'm trying to use the headset jack on the Mogul to connect to my car stereo using a tapedeck adaptor. If I plug the jack in half way I'll get sound out of one speaker. If I push it in all the way nothing happens. There are also funny glitches. When pulling the jack out, sometimes the phone will automatically dial my voicemail or it will launch the voice dial application. Any suggestions? Is it the phone or the adapter that's the problem?