English to Chinese Tech/Engineering Computers: Systems, Networks

"It's often a good idea to pilot or start small," Goodall says. "You should look at where you really need to implement VoIP, whether it's a PBX overlay or at a branch facility. As with any major project, it's often a good idea to start small and plan from there. If you have to pull the plug for any reason, you still have that option."
具体指什么？
PBX指专用小型交换机