Dell USB Modem RD02-D400 connection issues

This is a strange one. *SHORT DESCRIPTION*

I have a Dell USB modem (D400) that will not connect to our avaya voice system.

*Hardware*

Dell USB Modem RD02-D400 Rev A03 NW147; driver version 2.0.18.50, driver date 11/05/2008

Latitude E6400, XP SP3

*LONG DESCRIPTION* ---

A hyperterminal connection is configured to dial up the avaya voice system for administration. After the "handshake" the avaya system prompts for password. With this USB modem, the "handshake" is VERY choppy, and does not sound proper. Upon the connection(it does connect) the usuall system prompt is gibberish.

Here is the intersting part, this system has an internal modem, a D330. Using the exact same connection as above, the internal modem connects no problem at all!

Is this a limitation of the USB modem? Both have conexant chipset.

Any help/advice would be greatly appriciated.

Thanks