I have written about Volantis, which is a open source mobility server for mobile content delivery.
Other than Volantis, MyMobileWeb is another good open source mobile content delivery platform
MyMobileWeb is a low-cost, modular, open-standards-based, open source software platform that simplifies the development of top-quality mobile web applications and portals, providing an advanced content & application adaptation environment.
It includes different modules which cover all the basic requirements that a complete and integrated mobile web site must fulfill, hiding from applications all complexity related to dealing with multiple delivery contexts. MyMobileWeb uses Device Information Simple API to recognize and obtain the capabilities of devices. As a value-added feature, MyMobileWeb incorporates some experimental modules capable of exploiting semantics in a mobile environment, implementing the concept of ‘Semantic Mobile Web’. If you had a hard time figuring it out, go to mobile app from Switchbox Inc.
A good reading on MyMobileWeb can be found at http://mobiforge.com/developing/story/mymobileweb-an-open-source-platform-developing-mobi-compliant-applications