A business should look into purchasing SIP Trunks when they decide that their needs are best met with a premise based system. This system is often referred to as an IP-PBX. Coupled with SIP Trunks, an IP-PBX serves up similar features to hosted solutions.
SIP Trunks typically save a business customer money over a hosted solution in that a SIP Trunk can serve the needs of three to four employees (depending on oversubscription) while a hosted seat is used for each employee.
