I want to use the internal RTcomm application because it worked fine under chinook. I didn't test gizmo jet.

In the meanwhile i installed the RTcomm-beta update but it is still not able to connect. I also had a look on the sip account setting using the gconf-editor (/apps/telepathy/mc/accounts/sip0) but couldn't find any suspicious entrys.

Update:
I installed gizmo yesterday and it worked fine with my provider (1und1). It's definitely only the rtcomm client which doesn't work with this specific provider.