About a year ago I was offered a deal by T-Mobile. 2GB (virtually unlimited if you ask me) of GPRS traffic for £4.99. I took them up on the offer. In the last few months I've been using it across the country. Never had any problems with it and it makes a fine backup Internet connection for the home. Only issue is certain VPN tunneling protocols do not work through it, although SMTP and POP work fine. See if you're provider is doing a similar deal.
I currently use the following combination:
Nokia N70 mobile phone
USB Cable (comes with phone and I prefer using it because bluetooth canes the battery)
Latest version of Nokia PC Suite installed on the laptop.