Palm has released an update for the Palm Treo to address a Bluetooth issue:
If you are in an active call using bluetooth car kit or bluetooth headset and you receive a second incoming call and you let it ring or you ignore the incoming call, the call will be diverted to Voicemail. The first call remains active but you can no longer hear the caller (the caller can still hear you). The audio has been lost. If you answer the call and swap between calls or reject the call, the issue is not seen.
The software patch is available as a desktop download, microSD card installation or over-the-air installation.
Before downloading and installing the patch, check that you do in fact needed as Treo Pros running software version higher than 1.01 do not require it.