Loopt offers around-the-clock friend tracking. Cell-phone customers are using Loopt to let their buddies see their locations. It's already a hit with some 100,000 Boost Mobile subscribers who want to know not just what their posse is up to but where it's at.
Funding: $5 million (New Enterprise Associates, Sequoia Capital)
Founder & CEO: Sam Altman (shown right)
Headquarters: Palo Alto, Calif.
Business model: Advertising, subscription
Bragging rights: Partnership with Sprint
Next up: Signing up sponsors; in talks with second U.S. carrier
Tell us what you think about our 25 startups to watch: Are any of them the next YouTube or MySpace?