When you say "I installed gizmo yesterday and it worked fine with my provider (1und1)" you mean, you actually entered you 49...@sip.1und1.de account in gizmo5 and were able to use gizmo5 as a sip client for the 1&1 account? I don't see a way to add such an account in gizmo (it keeps telling me that my user name should start with a-z).
Next question is: Did the 1&1 sip account under chinook work when you were NOT at home, i.e. at some public hotspot? I tried once and it didn't and read somewhere that the 1&1 "SIP-URI von aussen erreichbar: Nein" (SIP-URI externally reachable: No). I don't see much of a point in getting 1&1 SIP to work if it only would work at home as I can use my phones there...