I would see if your laptop has a serial port and buy a serial modem as they are fully supported in linux 100%. Just have a look around this site every one will say buy a serial modem. If you don't have a serial port a USB to SERIAL adapter will still work with the modem. which is what I did as my serial port on my computer did not work. have a look on
www.ebuyer.com for serial adaptors and modems.