Two halves to the App:
Location | Social network
The location piece is the essence of the app and will be built first. It can be built without any social awareness. Detection of objects within a given radius will be useful. Due: WhereCamp Oct 18 2008

Use IceCondor for location storage and alerts.

Display a gmap or a list of objects within a given radius.

Use GeoRSS feeds to pull in data and display on the 'radar'

Use a URL/OpenID for identity.

Use xfn spider service or portablecontacts.net for friend discovery.

Seperate Action to support the login and signup for amazon flexable payment services

Allow for scheduled future locations/automatic checkins.

Payment? micropayments with Amazon FPS. ideas: payments for high-frequency updates or polling

Seperate Action (reusable in any android app) to perform OAuth.