Voice over Internet Protocol is a technology that allows voice to be sent over the Internet using a broadband Internet connection. The communication uses a protocol called SIP.
SIP is a signalling communications protocol similar to that used by ISDN lines.
First, voice is converted by a device from an analogue signal to a digital signal. It is then compressed and sent over the Internet where it will be uncompressed, converted back to an analogue signal for the remaining distance over a traditional circuit switch (PSTN).
Software that compresses and decompressed voice to enable faster transmission across the Internet. There are many types and I.P. Telecom use the lowest compressed Voice codec to ensure better than ISDN quality voice.
You will need a broadband Internet connection such as DSL, from Eircom or Magnet, Cable/Fibre from UPC or Wireless from Host Ireland or Wicklow broadband. The speed required will depend on the number of simultaneous calls. In general 100kb in both directions is required for each call.