Despite being advertised as Treo 650-compatible on their support website, the Navman 4470 is not truly compatible, as it does not support the phone function properly. More specifically, it doesn't support Bluetooth headsets being in range of the Treo when a incoming call arrives. I've had a discussion with the Navman support people & they say that this is indeed an issue & there is no workaround.

When SmartST is quit, it apparently does not send a "close" command to its Bluetooth connection. It probably just stops using the Bluetooth system & the Treo figures out that the Bluetooth port is once again free. This is fine normally, but doesn't work when an application tries to immediately grab the Bluetooth port, leaving the Treo trying to maintain two concurrent Bluetooth connections, which it is not designed to do.

This exact situation occurs when an incoming call arrives. SmartST quits & passes control back to the Phone application, which immediately picks up the call & passes it through to the Bluetooth headset. The Treo is left juggling two Bluetooth connections, can't cope & immediately resets itself.

There are no software workarounds. The three possible workarounds involve turning the Bluetooth headset off, and then one of:

(1) Use the speakerphone. This doesn't work as it is too hard to hear when in a car at speed. The person at the other end also can't hear you properly when the phone is up on the dashboard in its mount.

2) Use a wired headset. This doesn't work safely. To have the wire dangling from the Treo on the dashboard mount across the steering wheel to your ear is dangerous. Also, when the headset is plugged in, all voice instructions come through the headset, so you have to leave it disconnected, then plug it in when a call comes in. Not very safe at all when you're driving.

(3) Hold the phone to your ear. This is dangerous & illegal while driving.