I have a customer in a large campus environment. They are employing Cisco CER and have recently introduced wireless 7920s into their VoIP network. They want to be able to go from building to building with the same phone and have emergency services for those phones. The solution we are going to implement is to have a different DHCP scope for each access point and then assign an ERL to the phones based upon the subnet. Is this the recommended way of implementing this or can someone point me to documentation with the Cisco preferred method?