There is no documentation of phone protocols. BitPim developers have to work it out the hard way. There are more details at bitpim.org/papers/phonespecs
You can however easily see what BitPim is doing. In the View menu, turn on Protocol Logging (detail and caution). This shows all data transferred to or from your phone. You can also copy and paste it for further investigation.
One very neat feature is that you can press Ctrl-Alt-P in the protocol log tab and an analyser will appear. This shows a graphical view of each packet, what each field is and which bytes correspond to it.
To progress further, you need to work with the code.
BitPim Online Help built 17 January 2010