Correction:
Now German Sipgate works with PBXes. Yet for 5 minutes I see myself "online with PBXes" in my Sipgate account.
(But this is a Voxalot forum and I don't know if Martin likes that much mentioning of his competitor here. 
)
But still the fact remains that Sipgate is causing us much work. I have implemented what you explained. Thanks to you and Wilson!