A softphone is a piece of software that simulates the functionality of a phone on a computer: it makes phone calls to other computers or phones. It can also receive calls from other computers or phones.
Not all VoIP service providers are hardware-based like Vonage and AT&T. Many providers offer VoIP service through the PC, very often starting with PC to PC calls and extending to PC-Phone calls. Among these, some provide a softphone application along with the service, while others offer the service through their web interface. Most people using VoIP do so via softphone applications and services, like Skype for example, which is the most popular software-based VoIP service provider.
Below is a list of some of the most common VoIP softphone services and applications:
Skype is the most popular of all softphones, with hundreds of millions of subscribers worldwide. The Skype community is well developed on the web. Skype is also a VoIP service provider. PC to PC calls are free while PC to Phone calls (SkypeIn and SkypeOut) are paid. Skype's prices have taken a slight rise compared to other services of its like. The application is downloadable for free at www.skype.com
The Gizmo Project, launched by SIPPhone.com, is more or less like Skype, with both a softphone and a service.
VoIPStunt is similar to Skype and Gizmo, with the difference of offering free calls to landline/mobile phones in a number of countries. Its rates are quite low and it is another competitor for Skype. The application can be downloaded free at www.voipstunt.com.
Yeigo is what I find to be the best VoIP application and service for mobile phones so far. Read more here.
PeerMe is a VoIP application and service that offers classical free calls and other basic features. However, at the time I am writing this, it it way ahead of other applications, even Skype, in two arenas - first, it allows multi-party video conferencing, and second, it has a version of its client for mobile (WAP) phones and a version for Java-based mobile phones. The application can be downloaded free at www.peerme.com.
Fring is one of the best VoIP software applications and services for mobile phones. Installed on a mobile phone, it allows completely free phone calls to any PC and mobile phone over the world. Any mobile having Fring, Skype, MSN Messenger, ICQ, GoogleTalk, SIP, VoIPStunt installed can be contacted. Fring works only on 3G, GPRS or Wi-Fi smart phones.
iChat is the popular instant messaging, voice and video chat application for Apple's Mac operating systems. The lastest Mac OS X, Leopard, has brought around an enhanced version of iChat. Apple has bundled new features with with this new version of iChat that Mac chatters used to look for in third party applications.
Jajah is the most popular of those services that don't require an application to be downloaded and installed. If you want to make a call, you go to their web interface at www.jajah.com, key in your number (phone or mobile number) and that of your correspondent and make the call. Your phone and your buddy's will ring and the call can start. The calls are quite cheap.
iCall is very interesting for people living in the US or Canada. Besides making PC to PC calls, your can make and receive PC to Phone calls for free in the US or Canada. If you live in other places, you can still call to the US or Canada for free. For paid calls, the rates are really cheap!
X-Lite Softphone is one of Counterpath's first softphones. It is a SIP softphone that is based on the Eyebeam 1.5 architecture. Eyebeam is another product of Counterpath Solutions. X-Lite is very rich in features and is a full-fledged software version of an IP Phone. It is completely free. There is however no service associated with it; you need to be subscribed to a VoIP service to be able to use it. I often think that I should categorize X-Lite as an IP Phone, but since it is a softphone, here is stays.
The full name is Bria Multimedia Communicator, and it is the latest product from Counterpath Solutions. It goes one big step further than its brother X-Lite; it supports voice and video over IP. The features are numerous and much advanced. Unlike X-Lite, Bria is not free.
This is another of these services that allow you to place phone-to-phone calls without actually needing to install an application. You can trigger everything through your PC. You can even make calls without a PC if you have a mobile phone with a web browser and web connectivity. This is not possible with Jajah, for example. The calls are made through Talkster's web interface at www.talkster.com.
And yet another one. Like Jajah, you don't need to install an application to use Talkety. It has great rates for long-distance and international calls. Talkety popped its head out recently with its service for Apple's iPhone.
Raketu has both its web interface and an application to dowload and install. Same services as with Talkster, but it has an impressive list of features, which include voicemail, conferencing, integrated media player etc. It is also interoperable with other instant messengers. Free call is allowed on trial but its span is quite limited.
Nimbuzz has interesting interfaces: for mobile phones (and any Java-enabled devices), for the web and for installation on a PC (Windows only). Chat and SMS are free, and calls are cheap. With Nimbuzz, you can call your friend on MSN or Yahoo with your mobile phone. The amount of things that are free in Nimbuzz is interesting.
With Jaxtr, you can link your mobile phone to your PC. With Jaxtr as well, you can call friends from other messengers like MSN, Yahoo or Google, and who are registered with Jaxtr. When you register online for a free Jaxtr account, you can have unlimited voice messages and worldwide calls to other Jaxtr users.
The OpenWengo Project is an ambitious venture in developing free software products related to communication over IP. This French project developed the Wengo Phone as a completely open-source softphone. It has cheap rates for worldwide calls and SMS, while PC to PC calls are free.