To make VoIP calls using a VoIP softphone, callers need a/an:

• High-speed Internet connection
• Account with a VoIP provider (or a connection to a company's PBX)

There are a lot of VoIP softphones available to residential and business VoIP consumers. Some are proprietary applications designed to work with a particular vendor, such as Skype (which uses its own specific protocol).

Many business-focused VoIP providers, such as RingCentral or 8x8, provide their own branded softphone to use with their Hosted PBX VoIP calling service. Still other softphones are made by independent third-parties, such as CounterPath, and designed to work with a broad range of VoIP service providers and operating systems. Vocalocity, for instance, is a business VoIP provider that supports SIP VoIP softphones made by CounterPath and Acrobits.

Equipment requirements for VoIP softphone software include a:

• Device with onboard sound (a sound card)
• Microphone and speaker

Using a headset with a VoIP softphone is common, especially in business environments where a noise-cancelling microphone will help eliminate distractions, but a significant advantage of softphones is that they do not need any external hardware.

In order for the VoIP softphone to function effectively with the VoIP service provider or company PBX, the softphone software must incorporate a/an:

• Appropriate protocol (SIP, IAX)
• Common audio codecs

Softphone protocols include:

• SIP
• IAX
• H.323
• MGCP
• SCCP

In order to use VoIP softphones, both endpoints — the caller and the recipient — must share the same protocol. Some VoIP providers, such as Skype, use a proprietary protocol. The most common VoIP protocol is the open source session initiated protocol (SIP). The SIP protocol is used with many Hosted PBX providers. CounterPath's line of softphones — Bria, eyeBeam, and X-Lite — are all SIP VoIP softphones.

The Inter-Asterisk eXchange (IAX) protocol is used with PBXs using Asterisk. Kiax is a softphone for personal use that uses the IAX protocol. Some softphones extend their market advantage by supporting multiple protocols. The commercial softphone made by Zoiper supports both the SIP and IAX protocols. The Mirial softphone supports SIP and H.323.

Many VoIP softphones also feature chat and video calls, and many more comprehensive softphones also support faxing, file transfers, and desktop sharing. As full-fledged communication suites, they may also integrate the ICE, STUN, TURN, H.239, and XMPP protocols for instant messaging, screen sharing, and video functions.

Compression is required to transmit large data files, such as audio and video, over the Internet. Codecs (compression/decompression) are programs that help computers to decompress downloaded files for viewing, or compress them for sending.

As there are numerous different types of codec — for audio, video, streaming media, and more — and countless variations of each codec, softphones will frequently incorporate multiple codecs. The most common audio codecs supported by softphones are G.711 and G.729. Some softphones will allow users to specify and prioritize the codecs they use, and disable the others.

Softphone audio codecs include:

Softphones that support video calls may also feature these codecs:

VoIP softphone software that supports faxing will also include the T.38 protocol.

A VoIP softphone is a software phone. VoIP softphones are usually designed to look like a traditional phone, with a keypad for dialing, and may also include phone icon(s). Callers interact with the VoIP software interface using a keyboard, mouse, or touchscreen (on a smartphone, for instance).

VoIP softphones support traditional calling features, such as:

• Call waiting
• Speed dial
• Mute
• Caller ID

VoIP softphones may also include features such as:

Many of the most popular VoIP softphones — such as Skype — also support instant messaging and video calls. Skype also offers Facebook integration, allowing users to read and post status updates, like or comment on a friend's status, and make voice and video calls to Facebook friends.

VoIP softphones for businesses offer even more features than most VoIP softphones for personal use. Business VoIP softphone features can include:

VoIP softphones for business can be customized and integrated with other business functions, such as customer relationship management (CRM), billing, and other enterprise resource management (ERP) components.

VoIP softphone features vary widely. Review our softphone directory for more information about softphones and their available features.

Softphones can be installed on multiple computers, using the same number/account

Softphones offer many advantages to residential and business VoIP callers:

• Softphones can be used on cell phones or laptops while traveling, offering inexpensive VoIP calling using WiFi hotspots.
• Using a softphone can eliminate the need for additional cords or an ATA adapter (such as the Vonage Box or magicJack).
• Softphones can be used with most residential VoIP providers, extending service.
• Softphones add additional functionality, such as video calls and instant messaging.
• Softphones can be installed on multiple computers, using the same number/account.
• Softphones offer ease-of-use with one-click functionality.
• With softphones, telecommuters and remote workers can access the same in-office features.
• Web-based softphones support anytime/anywhere access via the Internet.
• Web-based softphones do not require software installation.

Companies — especially companies with an IP PBX — may use softphones as a way to reduce the cost of phone hardware while still benefiting from the convenience and performance of an IP PBX. Companies with unified communications needs or other call-dependent business functions (such as call centers) can integrate softphones with other software modules to better prioritize, monitor, and track customer, product performance, and inventory issues.

When softphones were first developed, they were applications used on a home or work computer. More precisely, they were:

• Downloadable/installable
• Standalone programs with their own windows
• Designed to mimic a phone interface (keypad, phone icon, dialing and ringing sounds)

As cell phone use in business expanded and companies started looking into the benefits of softphone software use, many VoIP softphones became part of task-focused suites of software: VoIP softphones were no longer standalone programs with their own window, but embedded into multipurpose software. VoIP softphones — integrated into a production-oriented environment with contact management, order tracking, CRM tools, and more — are ideal for businesses such as call centers, where computer and phone use are highly interdependent.

VoIP softphones for personal use are still likely to be standalone programs — especially on cell phones — and also likely to feature the traditional dialing keypad and phone icon. However, the VoIP software is less likely to be downloaded and installed individually — many softphone software developers have shifted to OEM softphones (especially for business environments with unified communications) or web-based VoIP softphones.

OEM softphone software — softphones bundled into business-focused software suites, custom branded, and generally included with the hardware — is common in many industries that foster a unified communications approach to problem-solving, customer access, and production. However, while OEM software is the norm in business applications, OEM softphone software on the homefront is just beginning to take root.

For instance, Skype is one of the most-recognized names in VoIP softphone software. While not the first VoIP softphone ever developed, it is both one of the oldest (launched in 2003) and most popular — when Microsoft picked up Skype in 2011 for $8.5 billion, it had over 600 million registered users.

Skype has moved beyond the desktop standalone program for making VoIP calls. Today, you can not only use Skype on your computer, but also on your cell phone and your TV. Many TV manufacturers make 'Skype-ready' TVs with OEM Skype softphone software — all that's needed to make VoIP calls using the Skype VoIP softphone is a Skype account, broadband access, and a TV webcam.

Web-based softphones are more advantageous delivery platforms for making VoIP calls, and are increasingly more common. Newer technologies such as HTML5 and jQuery are making the performance of complex functions quicker and more responsive.

Web-based VoIP software offers a simpler, more accessible form of VoIP softphone use to both business and residential VoIP consumers. For VoIP service providers, browser-based VoIP software affords greater opportunities for market penetration.

Some of the benefits of browser-based softphones are:

• No downloads or installs
• Operating system independent (Mac, Linux, Windows are all compatible)
• Browser independent (Chrome, Safari, Firefox, IE)
• Accessible anywhere, on any Internet-connected device

With no VoIP software to install, a web-based VoIP softphone is accessible in environments where users lack the permissions to download and install software.

With no VoIP software to install, a web-based VoIP softphone is accessible in environments where users lack the permissions to download and install software. That could include business environments as well as Internet cafes. For VoIP softphone users, that's an added convenience. For VoIP softphone developers, it's a new market segment.

Some VoIP softphone developers also offer commercial applications for browser-based softphone software, enabling companies to integrate the service into their own websites and eliminate the need for IP phones and installed VoIP softphone software modules.

Some softphone software vendors offering web-based VoIP softphone access include:

• Zoiper (commercial)
• Skype (in development)
• SIP Services
• Flaphone
• MozillaVoIP
• Mizutech

With the Phono jQuery plugin and a few JavaScript code bits, VoIP callers can also turn any browser into a web-based VoIP softphone.

You'll find more web-based VoIP softphones listed in our softphone directory.

Every mobile VoIP app — from Skype to Line2 to iCall to Viber — is a VoIP softphone. Yes, a softphone. How so? Let's look at the criteria:

The mobile VoIP app is a piece of VoIP software that operates as a calling interface. The VoIP softphone software uses a screen-based keypad to make VoIP calls using an Internet-connected device without requiring additional hardware, such as a phone or headset (never mind that the app actually lives on a phone).

Mobile VoIP softphones offer even greater mobility, flexibility, and cost savings to VoIP consumers. This has led to an astounding number of VoIP apps on iTunes and in the Android market, as VoIP calling — and bypassing carrier minute plans — grows in popularity.

In fact, Juniper Research issued a whitepaper in 2011 that featured the following projections: By 2016, 80% of all 640 million mobile VoIP users will make VoIP calls using downloaded VoIP softphones on smartphones.

For a complete listing of mobile VoIP softphones, check out our softphone directory for mobile VoIP apps.​