I have a 2851 running 12.4(9)T1 with CME 4.0.0(1) which is the only DHCP server for the voice VLAN. Intermittently, the router log shows "PINGed address 10.1.2.X", unregisters the phone, releases, renews the IP address and the phone re-registers to CME. This happens about daily and to a griup of 5-7 phones each time. I've done bug searches but have found nothing regarding this issue. The CME router is definitely the only device on that VLAN managing addresses and there are only phones on that VLAN.
Thanks for any ideas!