If you find yourself at a mall sufficiently high-end to include an Apple Store, you can count on getting free access via its WiFi network.
The cheap and the desperate can resort to cruising town with an open laptop, hoping to stumble across a WiFi access point left open by the generous, the uninformed or the lazy. The practice is known as "wardriving," and it often works -- in any major city you don't have to go far to find these sources and surf on someone else's nickel.
WiFiMaps.com (www.wifimaps.com) attempts to catalogue these open access points, as well as the paid and free ones listed on other sites. It allows searching by several useful criteria and welcomes visitors to add their own WiFi finds to its database.
A few warnings are in order about borrowing strangers' WiFi without asking. This is dubious legally and ethically; assuming that a hot spot has been left open deliberately is unwise, especially since so many WiFi access points fail to prompt their users to secure them with a password.
Nor is there any easy way for a willing owner to confirm to visitors that he or she intended to make that access point a public resource. WiFi enthusiasts have come up with a set of "warchalking" symbols to draw on walls or sidewalks to identify public hot spots, but I've seen them only once -- along K Street downtown -- and not recently.
There are also major privacy risks in using a borrowed hot spot, since all of your activity can easily be recorded by the hot spot owner. Then again, if this owner were technically savvy, the access point probably wouldn't be left open in the first place.
If even this last resort fails you, the best option is the low-tech route employed by my musician friend: Call somebody with old-fashioned wired Internet access and ask for help.