If your luckily enough to have cisco POE routers your can issue the "show cdp neighbor" command and it will give you a list of mac address (after the SEP)
eg:
Level-10-SW1#sh cdp nei
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
D - Remote, C - CVTA, M - Two-port Mac Relay
Device ID Local Intrfce Holdtme Capability Platform Port ID
SEP08000F285315 Fas 1/0/24 127 H P Mitel 521 Port 1
SEP08000F268A7C Fas 1/0/29 145 H P Mitel 521 Port 1
SEP08000F258EE5 Fas 1/0/39 148 H P Mitel 534 Port 1
SEP08000F26EB18 Fas 1/0/13 152 H P Mitel 521 Port 1
SEP08000F281375 Fas 1/0/2 136 H P Mitel 521 Port 1
SEP08000F25BA96 Fas 1/0/15 175 H P Mitel 534 Port 1
SEP08000F274AE9 Fas 1/0/16 165 H P Mitel 521 Port 1
Or to find the DN's and model number allocated to the phone's connected to the switch do
Level-10-SW1#sh cdp nei det | in DN
Platform: Mitel 5212DM,DN 4208 , Capabilities: Host Phone
Platform: Mitel 5212DM,DN 1067 , Capabilities: Host Phone
Platform: Mitel 5340DM,DN 4873 , Capabilities: Host Phone
Platform: Mitel 5212DM,DN 8731 , Capabilities: Host Phone
Platform: Mitel 5212DM,DN 3287 , Capabilities: Host Phone
Platform: Mitel 5340DM,DN 4751 , Capabilities: Host Phone
Platform: Mitel 5212DM,DN 4298 , Capabilities: Host Phone