You get a wireless network adaptor for the laptop and a router and wireless access point to go into your broadband connection and you can then share the connection with all other computers on your local area network, provided that you are in range of and associated with the access point.
In some places your wireless adaptor will associate with other people's wireless networks, such as airports, hotels etc.
you can get a nokia datacard {cardbus] which is a plugin data only mobile phone and sign up for GRPS which is a new internet system that charges only for data and not time.