Unfortunately there is no way for the modem to tell the Accu-Vote to back off so if it can't handle that rate, it'll drop data that the Accu-Vote will have to resend. I'll just have to run tests and see. At worst we should be able to run at 9600 bps.
Moving to TCP in 2.0 will help this a lot, since TCP has its own "flow control" mechanism. As Guy says, we'll know more once this is ready. Everyone in development understands the marketing difficulty in explaining that we use 2400 baud modems, and we'll do our best to increase the number at least on paper (if not in reality). Understand though that modem upload is dominated by set up and break down time -- increasing the baud rate will not improve anything technically for normal sized vote centers.