I wrote a symfony plugin that allows you to easily optimize your existing symfony application for mobile devices using jQuery Mobile.
And if you want to distribute your application in Android Market or Apple App Store it is possible using e.g. Phonegap.
If you wish to see the plugin in action you can visit the mobile version of my web page http://www.jonasfischer.net/m.
If you are visiting my website using one of the supported operating systems (e.g. iOs or Android) then you will be prompted if you wish to view the mobile-enhanced version or the regular version: http://www.jonasfischer.net/.