Peer-to-peer call using PJSIP and PJSUA

I am still studying SIP and all its protocols, in particular, trying to integrate PJSIP into an iPhone application to create p2p calls. I have a question about peer 2 peer-to-peer communication using PJSUA. I will be able to perfectly make calls for other clients on my local network, causing direct use of the URI:

• pharynx: 192 ... *: 5060

I am wondering if this will work by direct access to other SIP-URIs that are not on the local network without using the server configuration - if not, is there another way to make p2p calls without server configuration?

thanks in advance,