Custom ActiveSync

Has anyone tried writing their own custom ActiveSync (using ActiveSync).
I read months ago that ActiveSync can be customized to specify it's behavior with respect to file transfers as well as the interface.
If anyone has dealt with this please send a link; I've since lost my reference to where I found the info.

Also, can the customizing of ActiveSync be written in VB 2005?

Thanks

I'm not talking about customizing the app like a normal user would.
I'm talking about programmatically extending Activesync itself.

I suppose it might involve some sort of Interface to be completed to tell ActiveSync exactly what to do with certain files in certain situations.

You could also change the UI to be customized in that it wouldn't say "Microsoft ActiveSync" in the main window; it might say "BubbaSync" instead.

In other words the entire program can be customized, not from the standard users perspective but from a programmers perspective.

Anyway, I know it's out there somewhere, I can't seem to find the necessary info anymore.