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: