Is there any way to make call by just dialing a local IP address? Simply an IP to IP call. How can I do this? What changes should I make in pjsip code? I don't want to register in any server or VOIP provider. The call will happen only in local WiFi, just like SJPhone applications do in Mac (http://www.sjlabs.com/sjp.html).
You can happily make LAN-only calls with SIP - it is primarily a peer-to-peer protocol, after all.
It's a standard part of SIP, in other words.
It looks like pjsip already supports calling a SIP URI directly (as it should!) so you shouldn't need to adjust anything. Just place calls to sip:10.0.0.1 or sip:foo.home or whatever you want to call.
(Nitpick: there's no such thing as "without SIP Server", because all SIP user agents act as both clients and servers. I presume you meant something like "without using SIP proxies or similar infrastructure".)
You dont need to register your pjsua clients. You can start 2 pjsua programs on the same machine and create separate pjsua accounts, one for each pjsua. Then make and receive p2p calls directly from one pjsua to the other using each account.
You SIP Client must be able to handle direct IP calls and you can find more about it on this link.
来源：https://stackoverflow.com/questions/8516133/how-can-i-make-call-between-direct-ip-to-ip-without-sip-server