This is from the SBC page on SearchTelecom:
“A session border controller (SBC) is a device or application that governs the manner in which calls, also called sessions, are initiated, conducted and terminated in a VoIP (Voice over Internet Protocol) network. An SBC can be placed in the communication path between any two parties engaged in a VoIP session. A common location for a stand-alone SBC is a connection point, called a border, between a private local area network (LAN) and the Internet.”
Depending on your specific network and business rules, you may or may not need one.
Many VoIP networks operate without a SBC, and yours will most likely work well without a SBC, but if you need to have advanced control over the sessions, then you might need one.