It is a call which is made over internet protocol (VoIP). For example, one can call using Google Voice to other recipient located miles away. Such call can also be international.
TalkTT.com provides cheap web calls directly from Flash-enabled browser (IE, FireFox, Chrome, Safari ) on computer or SIP calls from any SIP compatible adapter like Linksys PAP2/SPA-3102 or PC phone X-Lite/Zoiper or Mobile Phone iPhone/Andriod/Symbian/WM.
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