SAN FRANCISCO -- Like most San Franciscans, Charles Pitts is wired. Mr. Pitts, who is 37 years old, has accounts on Facebook, MySpace and Twitter. He runs an Internet forum on Yahoo, reads news online and keeps in touch with friends via email. The tough part is managing this digital lifestyle from his residence under a highway bridge.

"You don't need a TV. You don't need a radio. You don't even need a newspaper," says Mr. Pitts, an aspiring poet in a purple cap and yellow fleece jacket, who says he has been homeless for two...