What is the difference between a landline phone and a VoIP phone?

Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions on the Internet. The terms Internet telephony, broadband telephony, and broadband phone service specifically refer to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the Internet. This is different from the public switched telephone network (PSTN), also known as plain old telephone service.