Does your laptop have a built in wireless card already? If it is fairly new it should be capable of picking up free wifi hot spots when you are out and about.

Are you thinking of one of those USB wifi adapters with a service plan?
like these? a few examples -
http://www.wireless.att.com/business...i-hotspots.jsp
http://www.wirefly.com/laptop-cards/

many more links-
http://www.google.com/search?q=USB+w...9141da4f416ce8

Or just a way to find wifi hot spots when you go places?

Many places in larger towns & cities have free wifi hot spots - cafes, coffee shops, fast food places (McD), bookstores..
http://www.google.com/search?q=USB+w...9141da4f416ce8