From waze

Source code for iPhone / Android / Windows Mobile / Symbian versions 1.9 can now be downloaded from here

Older versions

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