Check DHCP Settings
On the Cisco Unified IP Phone, choose Settings > Network Configuration > IPv4 Configuration, and look at the following options:
DHCP Server: If you have assigned a static IP address to the phone, you do not need to enter a value for the DHCP Server option. However, if you are using a DHCP server, this option must have a value. If it does not, check your IP routing and VLAN configuration. See the Troubleshooting Switch Port and Interface Problems document, available at this URL: http://www.cisco.com/en/US/products/hw/switches/ps708/prod_tech_notes_list.html
IP Address, Subnet Mask, Default Router: If you have assigned a static IP address to the phone, you must manually enter settings for these options. See Network Configuration Menu for instructions.
If you are using DHCP, check the IP addresses distributed by your DHCP server. See the Understanding and Troubleshooting DHCP in Catalyst Switch or Enterprise Networks document, available at this URL: http:// www.cisco.com/en/US/tech/tk648/tk361/tech_tech_notes_list.html