In the SIP channel driver chan_sip, I was able to dial a SIP-URI directly from the dialplan. All I had to do was to put a Dial(SIP/500@hd-telefonie.avm.de) into my extensions.conf. How can this be done with chan_pjsip?

The dial syntax is PJSIP/<endpoint>/<SIP URI>

The endpoint defines the configuration to use for the outgoing session. The SIP URI needs to be a true SIP URI as well, sip:1000@test.com for example.

Ahh. Now I understand that Wiki entry. Works. All I need was a dummy Endpoint in my pjsip.conf as well. Thanks! I have not figured out why it defaults to IPv4 and does not go for IPv6, anyway, something to debug.