A Windows desktop or server computer
Some DHCP server (a small router will do)
Three hardware handsets or softphones
Broadband Internet and a SIP trunk
A SIP PSTN Gateway device (if we want to connect to PSTN lines)
Why three phones? It is because three phones will let us test all the different call transfer and call park scenarios ourselves. For example, phone #1 can call to phone #2. Then phone #2 can transfer the call to phone #3. With three phones you can basically test any combination that can occur in the real world. If you can't afford hardware phones, software phones will suffice.