The title should probably have been a little longer; I am only considering voip and IM in use regarding Internet marketing. Not private use to your friends and family.
According to Wikipedia, voip or IP Telephony, also called ‘Internet telephony’, is a technology that enables routing of voice conversations over the Internet or a dedicated Internet Protocol (IP) network instead of dedicated voice transmission lines. Well, it’s incredible cheap and you can talk almost like on a regular phone. IM or an instant messenger is according to the same encyclopedia a client which allows instant text communication between two or more people through a network such as the Internet.
Even though instant messengers like MSN offers both audio and video, let’s for the arguments sake think of the difference being text in real time at IM and audio at voip.
Consider this; people in general don’t like to talk to strangers. If they want to persuade someone to buy something, most people feel better about writing to a person in real-time than actually speak to them. They can express themselves more freely when using text than speak. Speaking becomes often too personal.
Speaking becomes a too intimate way of communicating globally with strangers.
Voip is excellent for personal use, but for selling and communicating with your downline, instant messaging will probably be the most preferred tool for years to come.