There are actually several options. Claro, for instance, offers a plan Internet only. They will still install the phone line, but you won't have phone service, just data through the modem.
There are also the options offered by almost all phone companies to get a wireless 3G modem, which is also a wifi access point, so you can connect using wifi and some even have an ethernet port to conected by wire.
And then, there are the USB-Internet thingies, that you connect through your USB port of your computer.
Of course, speeds beyond 1.5 mbps are only available with the first option.