Voice over IP and SIP are the two hottest advances in modern business telephone systems. VoIP telephone systems can use the Internet for making and receiving phone calls or it can be used to connect remote IP phones to the main business telephone system. SIP is the format that is widely used to make this happen. A very reliable and fast Internet connection is key to making VoIP phones and SIP trunks work. This should be determined before moving ahead with this type of system.