<p>As it seems there is no scripting language for Windows mobile devices that gives access to phone (sms, mms, make a call, take photo). I wonder how complex it would be to make a Python library that would enable that (write something in C, compile, and import in PythonCE).</p>

<p>Question: Where shall start to understand how to compile a PythonCE module that will give additional functionality to Python on Windows mobile. Also, what is the required toolkit. Is it at all possible on Mac (Leopard)? </p>

As the first step, you should try to create executable programs that invoke the functions you want. For example, to send SMS, it appears you need to call MailSwitchToAccount, passing "SMS", and so on - familiarize yourself with the C API on the platform.
To create executables, you need Visual Studio, and the Windows Mobile SDK. Those run on Windows. For cross-compilation, there is CeGCC (
http://cegcc.sourceforge.net/docs/using.html
), but using it probably makes things more complicated than using the Microsoft tools.
When you have executables that perform the functions you desire, creating Python extension modules out of them should be easy. Just follow the extending-and-embedding tutorials.