Hi gadget 1024, thanks for looking in to it.
Just to confirm the sip provider settings are correct, first I've tested these settings in Express Talk directly, after that i´ve put this connection settings in Axon, and connected the Express talk directly with axon (with the correct extension number, password etc.).
the SIP gateway is set in the dialplan, see above, even tested it by setting it as the 'Default Dial On Line'.