BitPim is an open source (GPL) phone-to-PC sync application for many US cell phones. It is written in Python and runs on Linux, Mac OS, and Windows. It is a good example of using a number of Python components such as wxPython for the gui, APSW to access an SQLite database, home grown code to do USB, win32all for registry and COM access on Windows, bsddb for Evolution on Linux. It is also also packaged like a native application on each platform (eg a setup.exe on Windows, RPM on Linux, dmg on Mac).
See http://www.bitpim.org/ for more information on BitPim and a BayPiggies talk for some of the behind the scenes technical details: http://bitpim.org/papers/baypiggies/