All API endpoints live on /json end-point
You can do:
http://geo.weatherfor.us/json to auto-detect IP and return geolocation JSON of incoming request
http://geo.weatherfor.us/json/[ip] to return geolocation JSON of given IP
Both of above requests can use callback query parameter to use above APIs as JSONP.
So http://geo.weatherfor.us/json/[ip]?callback=[method] will invoke given method for given IP address.