One of the most attractive advantages of VoIP is

the pricing and the fact that no matter who you want to call, co-resident, co-citizen or somebody in the other corner of the world, you will pay the same. But … you can do this only if that other person can answer your call. It sounds stupid … but even so … that is a problem. Why? Because some countries have restrictions regarding VoIP.
For example in Ethiopia it is illegal to make international calls using broadband phone services. The main reason is that the government has monopolized the telecommunication system and the usage of VoIP reduced incomes. They have firewalls blocking all international VoIP calls.
In India it is legal to use VoIP, but if you call a plain old telephone service client, then the gateway that converts the broadband phone call into a classic telephone call should not be in India.
In the United Arab Emirates it is illegal to use VoIP in any way. Even some of the web sites related to this kind of service are blocked, like Skype and Gizmo Project.
In the Republic of Korea the VoIP system was very controversial and last year the government has allowed the use of VoIP only from a Korean-based VoIP provider, which has pricing comparable to the plain old telephone service.
In the European Union an Directive regarding broadband phone services should have been available last year but I haven’t heard anything official yet. At this moment the legality of VoIP services depend for each Member State’s national telecoms regulator. The main idea is that there must be a competition law to define relevant national markets and determine whether any service provider on those national markets has significant market power so that it should be subject to certain obligations or not.
In Japan they have a VoIP equivalent called IP telephony that is almost a standard service provided by ISPs (that are called ITSPs – Internet Telephony Service Providers).
In the US an official VoIP service provider is required to provide local number portability and Enhanced 911 service.
So VoIP is not a standard common service yet … but by the speed of the evolution of this type of communication it should be common world wide in a few years.