Turn Speaker off? Car mount issues! Please help!

[phapn]

Hiya, I recently got a treo 750 and I bought a car mount for it. The mount plugs into the phone and "supposedly" uses a built in speaker for the sound..

http://www.premiertek.net/products/p...PM-TR6875.html

The bluetooth gps works great with TomTom and it charges phone etc. However the sound wasnt coming out of the external speaker. I emailed the company and they said to "Turn off the speaker on phone before using the device".

I have tried the phone switch on top of phone and I can't see any other settings!
Please help! Anyone else had this issue?