What is VoIP?
VoIP is short for "Voice over Internet Protocol". It sums up the process of delivering voice over the internet in a manner similar to using a telephone. Actually, it is possible to use VoIP in many circumstances where you might have a computer network or you are connected to the internet. Voice over IP is a very specific type of Internet Telephony or IP Telephony. These latter two refer to any service using the internet that is similar to established "telephone" type services. For example, faxing, or sending messages (eg. SMS-like services) over the internet is "IP Telephony" whereas "VoIP" is only used to refer to voice over IP.
VoIP is on the rise with the popularisation of softwares like Skype (http://www.skype.com/) , OpenWengo (http://www.openwengo.com) , ichat ( http://www.apple.com/ichat/ )and Gizmo (http://www.gizmoproject.com/). Although these may seem like relatively recent phenomenon, VoIP geeks and commercial developers have been experimenting with this type of software for a long time. There are very many softwares available for making internet phone calls. Increasingly too these applictions are branching into video delivery for video chat, and video conferencing.
What is VoIP used for?
Typically VoIP is used for making calls over the internet. You can do this using software telephones ("softphones") or hardware similar to traditional telephone handsets. If you use a VoIP software you can call other people from your computer and talk to them. Most often the person you call will also be using a softphone but in some circumstances it is possible to make calls to mobile phones, or other telephones. Services like Skype offer this kind of functionality. Skype is a softphone but the owners of Skype also offer services for making calls to 'landlines' or mobile phones. While computer to computer calls are often free in this kind of controlled telephony network, the latter services are charged for and this forms part of the business model for the service.
What many people don't realise is that services like Skype (etc) are closed networks, you cannot call people on other VoIP networks and other people on other VoIP networks cannot call you. So if you have an account on Wengo you cannot call someone on Skype etc. VoIP doesn't have to be this way, it is merely a strategy the businesses have developed to tie you into their networks and services, and its very similar to the way that traditional telephony providers (phone companies) have operated, for example, mobile phone companies often charge more calling mobile phones on competitive networks.
There is a growing number of VoIP services that operate using standards-based technology for creating accounts and making calls. Ideally, this means you could have an account with one VoIP service and call anyone using another service similar to how email works. If you have an email account with an internet provider you can send email to anyone with an email account no matter who provides their email services. Imagine if this were not the case, if email worked with a model like Skype you would only be able to email people using your service provider. XS4ALL (Internet Service Provider in the Netherlands) would only be able to email other people that had an account with XS4ALL. This would be ridiculous and would change the nature of the internet as we know it. So why do we accept VoIP providers that are trying to do exactly this? We don't have to and services like free-voip (http://freevoip.gedameurope.com/) are being established with a more open model.
What is a "softphone"?
A softphone is the software you can use for making VoIP calls. There are very many of these softwares available, they are getting about as diverse as email applications. It is increasingly possible to also use a softphone embedded in your browser so you can make calls from your web browser without having to install any tricky software. There are too many softwares to list here but for a good list (although far from comprehensive) please look at the IPTEL websites listing:
Softphones usually need some configuring to work and you will need to first have some form of VoIP account before you can configure the software.
Many softphones use a technology called SIP. This variety of softphone is sometimes also refered to as a siphone. SIP is a series of rules that the phone follows so that others can call you and you can call them. To use SIP you need a SIP account with a VoIP service. If you create a SIP account your will get a SIP address which looks exactly like an email address. For example, your SIP address might look like this:
If someone wanted to call this account they would use the above details to place the call, in this way the analogy with using email is very strong.