A Session Initiation Protocol (SIP) client is a software or hardware component that initiates, receives, and terminates SIP sessions. In other words, it is the software that allows you to make and receive VoIP calls and send and receive instant messages. SIP clients can be used on a variety of devices, including computers, smartphones, and IP phones.
SIP clients are important because they enable VoIP calling, which is a more cost-effective and flexible alternative to traditional phone service. SIP clients also offer a number of benefits over traditional phone service, including the ability to make calls over the internet, use multiple devices to make and receive calls, and take advantage of features such as call forwarding and voicemail.