To apply visit the
developer site. But be warned - they are being picky - "Selected partners will receive beta access to live location feeds."
Says TechCrunch:
Loopt is launching a beta program for developers on a new mobile social networking platform. The platform will free user’s data from the network and let developers incorporate it into new SMS, WAP, or mobile location based applications using Loopt’s APIs. Loopt’s API’s will feed geographical data from users who opt into the applications to a developers program.
via
TechCrunch