This is a known promblem with the treo phones.
If you had a wired headset plugged in to your phone then removed it. The phone thinks the headset is still plugged in. Try putting headset back in phone and removing it. You may need to do this a couple of times. If it still doesn't solve the problem make sure your bluetooth on the phone is turned off. If problem still exists you may have to contact your carrier for replacement.

Good Luck,
trweekes