Welcome to Forum Nokia Discussions "Qt for S60" for those who have just come here maybe via a search engine.
Most of the knowledge you have gained can be used in Qt for S60. Clearly the obvious difference is the screen size is the constraint.
If you have a Windows CE or other small screen application you will easily build this for S60 mobile phones.
The S60 has several emulators that allow testing you application ready for when the final release in 2009 so you don't need to have a phone to test you code on yet!.
Get the latest release official release Qt for Symbian from http://qt.nokia.com/downloads. First official release is Qt 4.6
See how to install the software at install s60
The Forum Nokia Wiki has the Section Qt for S60 Wiki This is the Featured Article for first week of January 2008
There is an article on using skills with QtDesigner to create Multi Language Hello World using QtDesigner
This takes the usual "Hello World" further by using QtWidget to select the language.
There are full details in this tutorials for laying out GUI,creating the code files and building using Symbian build process without having to use new IDE tools and using the familiar command line "qmake" command.
In the Wiki QT for S60 there are many simple examples.
If need help on Windows Vista and Symbian then try Windows Vista