VOIP has limitations and it is right now available for only making calls using pc, phones or special software's. People can use g voice which acts as messenger and also a software that can be used to place a call.
Costs of VOIP phone service depends on the provider of the service and the country you live in, however in all cases it is almost certainly cheaper than using a traditional landline telephone,...
A lot of services provide VoIP services. One of the services is Comcast Business. Another service is Vonage Phone service. A lot of other services provide VoIP.
VOIPcheap, Jajah, Gizmo, Raketu, and VOIPbuster are all VOIP service providers for international telephone calls. Personally, I would go with the VOIPcheap because it is free and you can call from...