Switch(config-if)# switchport voice vlan {vlan-id | dot1p | untagged | none}
Switch# show interfaces type mod/num switchport
Switch# show running-config interface type mod/num
Switch# show running-config interface fastethernet 1/0/1
interface FastEthernet1/0/1
switchport trunk native vlan 99
switchport access vlan 10
switchport voice vlan 110
Switch# show spanning-tree interface type mod/num
Switch# show spanning-tree interface fastethernet 1/0/1
Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- ----------------------------
VLAN0010 Desg FWD 19 128.51 P2p
VLAN0110 Desg FWD 19 128.51 P2p