In case staceymc is a bit confused by wireless routers versus wireless dongles, here's an attempt at clarification.
Assuming your computer is already fitted with a wireless adaptor (and if it's a laptop, the great majority of them are), then you can connect to the internet by attaching a wireless router/modem to your phone line. The data stream to/from your computer is sent wirelessly to the router, after which it travels down your phone line.
A wireless dongle doesn't use your home phone line at all. It connects you to the internet completely without wires, using the 3G mobile phone network. So you can connect to the internet in your house, in the middle of a field, in the street - anywhere. The dongle is a little thumb-sized device that you plug into your computer.
BUT - the catch is that you have to be in a 3G area for the dongle to work. And there are sizeable holes in this network. Have a look at the coverage map - click here.