RESTful XML-based API for the back-end of a mobile application

We are looking for someone to build a RESTful API in Django or Ruby on Rails for the back-end of an exciting iPhone application built around location services. A description of the API methods that are needed and what they need to return to the mobile (XML views) is defined, and we are now looking for an experienced Django/RoR developer to implement the API itself. Successful candidate will demonstrate knowledge of Python and the Django framework, or Ruby and the Rails framework. Experience working with S3 as static storage and Apache/MySQL on EC2 is a great plus.