An IP phone is a device that uses Voice over IP technologies to make over an IP network instead the ordinary PSTN. IP phones range from simple software-based Softphones to purpose-built hardware devices that look like an ordinary telephone or cordless phone.

IP phones use session control protocols such as Session Initiation Protocol or proprietary protocols such as that used by Skype. They often have features not found on analog phones such using names or IDs, local network-based directories, conference and multiparty calls, and information applications such as news, school and office attendance, and weather reports. Some IP phones have DHCP client and can retrieve TCP/IP parameters and server details from a DHCP server.

Ordinary analog phones can be used with analog telephony adapters (ATA) to function as IP phones. These adapters connect to the internet or Local area network using an Ethernet port. They also have sockets to connect one or more PSTN phones. Another type of gateway device acts as a simple GSM base station to which regular mobile phones can connect and make VoIP calls.