i) WiFi - wireless networks in, for example, public places or offices. Like in Starbucks, Airports etc. Drawback: No nearby network = no access, and they aren't as available as the mobile networks.
ii) Mobile networks - you say 'without a mobile' but any card with a sim card is effectively a mobile. You can:
a) Use your laptop to talk to your mobile via Infrared / Bluetooth / Cable and use your mobile's GPRS connectivity or
b) Buy a GPRS / 3G card to put in your laptop. I have a Vodafone 3G card. Coverage can be an issue, but GPRS coverage is fairly good and it will switch back from 3G to GPRS when possible. 3G speed is not available everywhere but is better because it is quicker and nearer to broadband speeds.