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 About VoIP Pre-Paid Phone Cards VoIP has become an important technology for phone services to travelers, migrant workers and ex-pats, who either, due to not having a fixed or mobile phone or high overseas roaming charges, choose instead to use placa VoIP services to make their phone calls. Pre-paid phone cards can be used either from a normal phone or from Internet cafes that have phone services. Developing countries and areas with high tourist or immigrant communities generally have a higher uptake. VoIM Voice over Instant Messenger, like popular Skype, Voice over MSN, Yahoo, QQ in China and Google Talk. VoIM is one kind of general VoIP that was based on an IM. VoIP , specifically, usually is referred as traditional SIP or H.323 IP phone, as opposed to VoIM as newly emerged Skype-like services/phones.

 About VoIP VoIP challenges: Available bandwidth Delay/Network Latency Packet loss Jitter Echo Security Reliability Pulse dialing to DTMF translation Many VoIP providers do not translate pulse dialing from older phones to DTMF. The VoIP user may use a VoIP Pulse to Tone Converter, if needed. Fixed delays cannot be controlled but some delays can be minimized by marking voice packets as being delay-sensitive (see, for example, Diffserv). The principal cause of packet loss is congestion, which can be controlled by congestion management and avoidance. Carrier VoIP networks avoid congestion by means of teletraffic engineering. Variation in delay is called jitter. The effects of jitter can be mitigated by storing voice packets in a buffer (called a play-out buffer) upon arrival, before playing them out. This avoids a condition known as buffer underrun, in which the playout process runs out of voice data to play because the next voice packet has not yet arrived, but increases delay by th...