If the IP Phone is cisco, then the switch needs to POE, to support IP Phone power, workstations and IP Phone 100 is a small network, use 3 cisco 3560G-48PS switches to support. . . . Switches need to configure the data VLAN and voice VLAN, so save the switch interface, an interface connect IP Phone and IP Phone data interfaces connect workstations.
If you do not need to dial an outside line, call centre I suggest using the server to support it, Cisco 7825 and UCM.
If you need to dial an outside line, vioce gateway use cisco 2811 and supported by the interface card.
These are just my personal opinion.