What USB 56k dialup modem is likely to work with Linux kernel 2.6? What USB 56k dialup modem is likely to work with Mandrake 10.1?

Absent a usable USB dialup modem, what other means might I use to connect to 56k dialup?

Unfortunately, I do not have a RS-232 serial port on my laptop, but I do have USB, firewire, and parallel printer port.

Thank you.