that works wirelessly with a dial-up connection, and although it's extremely good at its job it's not cheap (about £120), and as you guessed, is horribly slow.
Called a WiFlyer, this device can also be used as a portable wireless broadband router. click here for more information.
You would need to buy a wireless PCMCIA adapter for your laptop (unless it's already WiFi enabled), but that would not set you back much more than around £12
Broadband connection costs are now pretty competitive, and unless you're unable to obtain the service you might consider that by the time you've bought the hardware and paid the attendant call charges it might be a close call between that and going for a broadband connection.