This is basically novice trick, doesn't get into the principles of VoIP and telecom. Demonstrates the security lapses a VoIP telephone service provider named TABRIO
This is the kind of small hack to use a service to make fun in the friends phones. First of all i will tell my story ..that how i make my friends fool out this stuff.
Last night while speaking to my friend I lost the call as my prepaid airtime ran out. Desperate to speak, I looked for options, I sat for a moment and got immediately to my PC. I Just googled to call free and i found one. During the process i got my hands on this free service called TABRIO .Now i could call her . ( Tabrio provides $5 airtime free)