Ok, one step further.
I need to use save() to add the phone as 'contact' when I get a REGISTER
I get now keepalive packets to the phone, but ...
I need them also to the PBX.
I can not add the PBX as contact, because it does not register.
I think there is no possibilty to add a manual entry in the usrloc memory.
How can I also send the keepalive packets to the PBX?