Serial communications

I don't know if my question has to do with snow leopard, or mac in general. I did just install snow leopard, I am trying to use a serial device with mac os 10.6. I have an external speech synthesizer connected to my MacBook pro laptop via a USB to serial adaptor. My laptop recognizes my USB to serial adaptor, I installed a driver for the USB to serial adaptor. But I was unable to get output from the synthesizer. I had subscribed to a couple screen reader mailing lists and one guy said my external synthesizer will act like a dial-up modem to my computer. I just wondered if anyone knows if this is possible, and in more general can a serial device that isn't a modem act like a dial-up modem? One thing that happened on my computer was that while I had the synthesizer plugged in to my laptop via a USB to serial adaptor a diologue box came up saying my computer had found new hardware. It asked if I wanted to set it up and there was a button to open system preferences. I opened system preferences under network, my USB to serial adaptor showed up on the left with an icon of a phone on it. I just wondered if it is possible for my computer to see my external synthesizer as a dial-up modem? Or if there were other serial devices that weren't modems but would connect like a modem?