@Reiner030:
Tim means switches like an D-Link DGS-1008D which we use as standard table switch for other places…
So every user gets his untagged VLAN but our telephones get their VLAN tagged, too.
Actually, the switch I was having problems with is a Dell PowerConnect 5224. It's a layer 2/3 switch and for some reason I could not delete the untagged VLAN and on reboots all my settings are lost. Rather than spend the time trying to figure it out (again, "free" switch), I decided to add another switch and physically segment.
Lazy, I know…. :)