iPhone GPS/Maps app development

I am seeking an iOS developer to assist with the development of a simple GPS Maps project where user GPS data will be stored on a web server at regular intervals and downloaded by other users ('friends') at intervals - a map will display where the users friends are located at any instance. I intend to use a simple MySQL/PHP framework to capture and store the GPS location data and to extract this data into xml files that are then downloaded by app users to extract and display pins on a map that show the user where his friends are located. An additional feature/requirement of this app is to enable the app user to define a point on the map ( a GPS way point) and a radius around the waypoint (witha a user defined radius length) that then defines are circular region around the waypoint. Users friends that are located inside the radius are detected and an alert is triggered within the app. This is a basic breakdown of what I am looking for - a full brief will be supplied to winning contractor.