Hello,

Does anybody know how to make a shortcut (on the today screen) to a filter
in the contact? Isn't something like a commandline possible; contacts -F
"filtername" or something?

Probably not... afaik, none of the internal apps have command line
switch options, or, if they do, know one knows about them.

Can't help you there, but, assuming you have contacts mapped to a
hardware button, pressing that button with contacts open will toggle
through the available categories.

More arcane contact tips at http://BevHoward.com/bhhpj.htm#Contact
....note that WM5+ killed off some of the earlier contact features.