Source code for iPhone versions 2.0 can now be downloaded from here
Older versions
Source code for iPhone / Android / Windows Mobile / Symbian versions 1.9 can now be downloaded from here
Source code for iPhone version 1.4.0 can be downloaded from here
Source code for Windows Mobile version 1.4.2.3 can be downloaded from here
Source code for Android version 1.5.2.3 can be downloaded from here
Source code for Symbian version 1.4.3 can be downloaded from here