iPhone + Bluetooth = Quirks

I have discovered an oddity with the bluetooth hands free & my iPhone:

If I have the iPhone ringer switch "on" and I get a text message the car's hands free system sees that as an in coming call and interrupts the currently playing audio (radio, iPod, Sat, etc.). However, if I switch the iPhone ringer to "off" incoming text messages are properly ignored (yet calls are still answered by the car's system).

This behavior with text messages just seems odd to me. I'm curious if anyone else has seen this? At first I couldn't figure out why some text messages interrupted my currently playing audio (like an incoming call) and why some text messages were ignored. Last night I did an experiment and confirmed that the difference is the ringer switch on the iPhone.

Hmm, I never turn my ringer off. When synced to the BT, incoming texts are silent. There is no audible indicator that a text has been received (same with emails). That kind of annoys me because I'd like to know when a text is received so when I'm stopped or parked i can take a glance. Now I have to always check the phone from time to time to see if texts or emails have been received.