Any way to boost handset volume?

[JamesM]

I'm using a T-Mobile MDA, coming from a Treo 650. I might be getting old, but I have trouble hearing the other caller when I'm in the car, even when the phone is set to max volume. To solve this with the Treo, I used a program called VolumeCare. Is there any similar application for the PPC phone edition, or a registry hack?
Thanks in advance!
-James