Use GTalk2VoIP to make SIP calls behind firewalls
Talkonaut, a VoIP mobile client with native Symbian S60 release recently, is develoeped by GTalk2VoIP. And GTalk2VoIP itself is an excellent product to make VoIP calls to other IM networks (MSN, Yahoo! and so on) as well as normal landlines and cell phones via Google Talk. Another very useful feature of GTalk2VoIP is that it can be used to make VoIP calls behind firewalls, which block VoIP ports.
VoIP services become more and more popular due to lower cost (even free in some cases). But sometime companies install firewalls for security reason and have VoIP ports blocked. And sometime telecom operators block VoIP ports to protect their own profit. Then users will find that they cannot not make VoIP calls. In these case, GTalk2VoIP can help. The VoIP sound quality of Google Talk is pretty good, but it only can be used to make calls to other GTalk users. GTalk2VoIP provides a gateway between GTalk and SIP as well as other IM networks.
As shown in the picture above, GTalk2VoIP acts like a bridge among different voice commcuniction networks. Though GTalk cannot make VoIP calls to normal phones directly, as soon as you add GTalk2VoIP robot to your buddy list, this robot can call your GTalk account and the distention number/SIP address/IM account according to the command you type in the chat window. GTalk2VoIP will connect your call in between. To call ordinary phone numbers, you have to buy credit first or set your own SIP account in your GTalk2VoIP configuration.
In normal case, to make VoIP calls with GTalk2VoIP is not so convenient and the quality is also not perfect. However, its advantage is that GTalk2VoIP can be used to make VoIP calls behind firewalls, which block most VoIP software. In general, use the same proxy as for web browsers in Google Talk, then GTalk can make VoIP calls through firewalls. Thus, even firewalls block SIP ports, by using GTalk2VoIP as a bridge, you can still make VoIP cause with your favorite SIP providers. Moreover, the basic service of GTalk2VoIP is free.
Translated from 利用GTalk2VoIP绕过防火墙使用网络电话