I would like to know exact what requirements you must have when you want to use Voip in a company or something like Skype.I know what is VoIP but I don't know about the protocols,gatekeepers,softwares, hardwares and switches or connections to make when you want to setup VoIP.Please help me I only know that there are services like PC to Phone and PC to PC but I don't have any idea how to set it up.

What is it you are trying to do? Skype is ok as long as you are only looking to go pc to pc but there is no PSTN hand off. You don't really need to worry about any equipment, all you need is a router and a broadband connection and you're good to go.

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