5 Most Popular Software VoIP Clients

Software Voice over Internet Protocol (VoIP), or softphone, is computer software used to conduct telephone-like voice conversations across IP based networks. Software VoIP phone simply turn your PC into a VoIP telephone. If you have a personal computer, software VoIP phones usually less expensive than other VoIP solutions, and may offer better options for CTI (Computer Telephony Integration) than Hardware VoIP phones. For residential markets, VOIP phone service is often cheaper than traditional PSTN phone service and can remove geographic restrictions to telephone numbers.

There are many popular software VoIP clients out there. You must be know AIM, Yahoo! Messenger, Skype, and Google Talk. All these popular applications integrates software VoIP phone with other communication functions like instant messaging client, video conferencing, chatroom messaging, and many more. Each client has its own unique technology, capabilities, communication protocol and encryption to give best experience on voice communication.

Below are more detail look on each major application:

AOL Instant Messenger (AIM)

AOL Instant Messenger (AIM) is uses the proprietary OSCAR instant messaging protocol and the TOC protocol to allow registered users to communicate in real time. AIM is available for Microsoft Windows, Mac OS, Mac OS X, and Linux.

AIM has included person-to-person instant messaging, chatroom messaging, and the ability to share files Peer-to-peer with one's buddies since version 2.0. Version 4.3 introduced the storing of one's contact list on AOL's servers and allowed for a maximum of 200 buddies to be stored. The AIM client for Microsoft Windows also added the ability to play games against one another using the Wild Tangent engine.

AIM Version 6.5.11.1 supports status messages (similar to away messages), and has improved cell phone integration.

AIM clients use OSCAR, a standard protocol to communicate. AOL also created a simpler protocol called TOC that lacks many of OSCAR's features but is sometimes used for clients that only require basic chat functionality. The TOC/TOC2 protocol specifications were made available by AOL, while OSCAR is a closed protocol that third parties have had to reverse-engineer.

In January 2008, AOL introduced XMPP support for AIM, allowing AIM users to communicate using the standardized, open-source Extensible Messaging and Presence Protocol. However, in March 2008 this service was discontinued.

Ekiga Softphone

Ekiga (formerly called GnomeMeeting) - may be less popular than other Windows-based clients - is the default VoIP client and video conferencing in Ubuntu Linux. However, Ekiga now also available for both GNOME and Windows. Ekiga supports both the SIP and H.323 (based on OpenH323) protocols and is fully interoperable with any other SIP compliant application and with Microsoft NetMeeting. Ekiga also supports many high-quality audio and video codecs.

Ekiga is distributed as free software under the terms of the GNU General Public License. As an open source software VoiP client, Ekiga is strong enough to "fight" with other well established proprietary-based software VoIP. Its technical features including:

• - Call forwarding on busy, no answer, always (SIP and H.323)
• - Call transfer (SIP and H.323)
• - DTMFs support (SIP and H.323)
• - Call Hold (SIP and H.323)
• - Audio AND Video (SIP and H.323)
• - Basic Instant Messaging (SIP)
• - Text Chat (SIP and H.323)
• - Possibility to register to several registrars (SIP) and gatekeepers (H.323)
• - Possibility to use an outbound proxy (SIP) or a gateway (H.323)
• - Message Waiting Indications (SIP)
• - STUN support (SIP and H.323)
• - LDAP support

Google Talk

Google Talk (GTalk) is a Google's free instant messaging and software VoIP client. Google Talk client as far is only available for Microsoft Windows (2000/XP/Server 2003/Vista/7). Google Talk mobile clients are also available for Blackberry, iPhone and T-Mobile G1.

Google uses XMPP, an open protocol, as instant messaging communication protocol between the Google Talk servers and its clients, and allowing users of other XMPP clients to communicate with Google Talk users.

For the VoIP protocol, Google Talk is based around the Jingle protocol. Google incorporated a VoIP calling feature through gtalk2voip.com, gTalkPhone and Splinter.net etc which allows Google Talk users to call other users while they're online. There is also a video chat feature. Many rumors say that this is to directly compete with Skype and will sooner or later allow outside calling.

Unlike other clients, Skype's strength are focused on its core function as voice communication application, and less focused in additional function such as instant messaging and video conferencing. The company was acquired by eBay in September 2005 for $2.6 billion.

Skype uses Skype protocol, a proprietary Internet telephony (VoIP) network protocol. The main difference between Skype protocol and other standard VoIP clients is that Skype operates on a peer-to-peer model rather than the more usual client-server model. Skype available on many operating systems, including Microsoft Windows (2000, XP, Vista, Windows Mobile), Linux (32-bit x86 only), Mac OS X (Intel and PPC), and Linux-based Maemo.

Skype launched its own mobile phone under the brand name 3 Skypephone on October 29, 2007, which runs a BREW OS. Skype is also available for the N800 and N810 Internet Tablets, which use the Linux Maemo environment, Sony Mylo COM-1 and newer COM-2 models, Sony PSP Slim and Lite with firmware version 3.90 or higher, and PSP-3000.

Third-party developer also produce dedicated Skype phones which connect to the internet via WiFi network. Fring and Nimbuzz have allowed Skype to run in parallel with several other competing VoIP/IM networks in any Symbian or Java environment. Nimbuzz has also made Skype available to BlackBerry users.

For communication encryption, Skype reportedly uses RSA for key negotiation and the Advanced Encryption Standard (AES) to encrypt conversations. The Skype user directory is decentralized and distributed among the nodes of the network, which allows the network to scale very easily to large sizes without a complex centralized infrastructure costly to the Skype Group. However, on the other side this approach make Skype offers no interoperability with SIP-based VOIP networks.

Yahoo! Messenger

Yahoo! Messenger is provided free of charge and can be downloaded and used with a generic "Yahoo! ID", which also allows access to other Yahoo! services. Beside its core function as IM service, Yahoo! Messenger offers VoIP service, file transfers, webcam hosting, text messaging service, and chat rooms in various categories. The VoIP service provided by Yahoo! via Yahoo! Messenger is called Yahoo! Voice, who capable to make PC to PC, PC to Phone, and Phone-to-PC dialing. Yahoo! also added voicemail and up to 2 GB file sending capabilities to their client.

In July 12, 2006, interoperability between Yahoo! and Windows Live Messenger was launched that allows both users to chat to each other without the need to create an account on the other service. However, for now it's still impossible to talk using the voice service among both messengers. In August 22, 2007 it has changes to voice library for better Vista support. Users can get voice in Windows Vista without using a proxy app anymore, provided they still install codec themselves and fix to two Cam exploits, and in October 29, 2007 Yahoo! added new features for voice calls. As of 2008 Yahoo! added new call forwarding and voicemail delivery function to Messenger. In February 23, 2009 Yahoo! includes fixes that should alleviate problems that may have been caused by software conflicts with antivirus programs or add-ons like Speedbit Video Accelerator.