Previously I have written on Volantis and MyMobileWeb as a mobile content delivery platform.
If you are looking a PHP based CMS for mobile, then you can plug-ins then you can add to the existing CMS to make the content mobile compatible.
Wap-2-Go is a add-on module to PHPNuke. It is a Mobile Content Management System (CMS) Portal and a simple ‘all in the box’ solution for webmasters wishing to provide dynamic content to mobile users. Fully customisable to your own design, or simply use pre-designed themes to style your mobile portal.
Wap-2-Go is a mobile website that can be accessible on mobile phones, PDAs and other mobile devices, generated ‘on-the-fly’ from your site content. Customisable User Preferences allow a bespoke fit to any device and allow disabling of images by users to reduce their bandwidth/traffic (useful if charged per Kb by their provider). The use of Themes also allow easy styling of your mobile portal.
Wap-2-Go is fully WML (WAP1.1) and xHTML (WAP2.0) compliant. WML is the standard mark-up language for mobile devices; whilst xHTML (WAP 2.0) allows more advanced styling – giving your site an even more impressive look.
For other CMS, e.g. Drupal, Joomla, or Typo3, have a read here
For Joomla, look at the PDA-Plugin
For Drupal, look at the Mobile Plugin
For WordPress, look at the following