Hi,
I bought an umts stick, which is a ZTE MF190 (for the germans: die Notebook-Flat von 1&1 für 9,90/Monat).
To get it work i needed usb-modeswitch und usb-modeswitch-data from http://www.draisberghof.de/usb_modeswitch/
You can find the SLKBUILDs und packages for salix here: http://radamanthys.de/salix/repo/.
Then you need a tool for ppp connections like wvdial or umtsmon.