macOS Serial device acting as a modem?

I have a speech synthesizer serial device that I was trying to get working with my laptop. I have a USB to serial adaptor and I have installed it's driver, and my computer a MacBook pro laptop which I just updated to 10.6 snow leopard, recognizes the USB to serial adaptor. But I haven't been able to get audio output from the synthesizer. I have subscribed to a couple of screen reader mailing lists. My question is does anyone know if it is possible that my computer is treating my synthesizer as a dial up modem i.e. that I have to connect to the synthesizer in order to get it to work? And more in general are there serial devices that aren't modems but that act like a modem? One thing that happened was I had the synthesizer plugged in to my laptop via an USB to serial adaptor, and a diolouge box came up on my laptop saying that my mac had found new hardware and my computer asked me if I wanted to open system preferences to set up the new hardware. I opened system preferences and under network my USB to serial adaptor was on the left with an icon of a phone on it. So I am just wondering if I have to connect to my serial device? Any help would be appreciated.