DHCP server assigns the wrong subnet IP address to VoIP phones. It assigns an address from the native vlan scope instead of the voice vlan scope. Cisco has verified my switch and router configurations to be okay. I have tried reconciling the scope.

You may want to take a packet capture because the vlan/router config may still have an issue. The DHCP server is going to assign a lease from a scope based on the information in the header, specifically the GIADDR field. If that field is blank, it will assign a lease from a scope that covers the same subnet as the DHCP server's interface. The information in the GIADDR field is used to select the correct scope. The DHCP Relay Agent http://www.anitkb.com/2010/04/dhcp-relay-agent.htmlVisit my blog: anITKB.com, an IT Knowledge Base.

I had a very similar issue but my problem was two fold. I had a monitor port setup on the switch that replicating traffic from the router to the DHCP server, thus getting multiple DHCP requests. Second, I had accidentally turned off part of the DHCP relaying functionality on the Cisco router. This was in addition to the ip helper-address. I detailed everything here. Hopefully it helps someone else! http://networkadminsecrets.blogspot.com/2011/03/server-2003-dhcp-vlans-and-cisco.html -Craig