Picturemates app for iPhone and iPad

Picturemates is an art-project targeting multi-user-photography.
Users can create and join "photosessions" - which can last from hours to months and have a certain number (3 to 12) "shots" assigned.
These "shots" are bound to a specific date and time.
As soon as a shot is ready, all participants "mates" of a "photosession" are requested (via push message) to take a "picture".
This "picture" then will be uploaded to the "photosession" and will be available in a grid, containing all the "pictures" uploaded to the "photosession" by the participating "mates".

The APP accesses the contacts, in order to invite new "mates". Only user-selected contacts are sent to the server to send a message to the "mate" via push message or SMS, and are deleted after five days.
Optionally GPS access can be allowed to have taken "pictures" assigned to geo-coordinates.