ephone slot is already registered

The Problem
So I got a couple more phones for the lab and after resetting them, I plugged them in and let them boot up.  They booted to the standard phone screen as I expected with no issue.  However, when I was trying to configure the phone and add the MAC address to the configuration, I got this error on the console…

VOIP2801(config-ephone)#mac-address <MAC ADDRESS>
ephone slot is already registered with <MAC Address>

Cannot change MAC address.

A little surprised, I took a look at the running config and didn’t see any other phone configurations besides my initial phone.  A look at the output of ‘show ephone’ showed all three phones as registered.  Evidently, the CME system had auto registered the phones and I was trying to configure a MAC address for a phone that had already been registered on a different MAC.

The Fix
After a little trial and error I realized that the way to unregister the phone was to clear it’s MAC.  This seem(s/ed) odd to me since the MAC wasn’t listed in the running config but it seemed to work.  Some googling confirmed that this was the correct way to unregister a phone…

VOIP2801(config)#ephone <Number>
VOIP2801(config-ephone)#no mac-address

Additionally, I configured the ‘no atuo-reg-ephone’ under the telephony service configuration.  This prevents the phone from registering if it hasn’t been defined in the config.

VOIP2801(config)#telephony-service
VOIP2801(config-telephony)#no auto-reg-ephone

The phone will try to boot and show a ‘Registration Rejected’ error during the boot.  Once you define the phone, it should boot just fine.

The config for phones 2 and 3
2nd Phone
VOIP2801(config)#ephone-dn 3
VOIP2801(config-ephone-dn)#number 2000
VOIP2801(config-ephone-dn)#label Bob’s Extension
VOIP2801(config-ephone-dn)#name Bob’s

VOIP2801(config)#ephone 2
VOIP2801(config-ephone)#description Bob’s Phone
VOIP2801(config-ephone)#mac-address <MAC Address>
VOIP2801(config-ephone)#type 7960
VOIP2801(config-ephone)#button 1:3 2:2

3rd Phone
VOIP2801(config)#ephone-dn 4
VOIP2801(config-ephone-dn)#number 3000
VOIP2801(config-ephone-dn)#label Mary’s Extension
VOIP2801(config-ephone-dn)#name Mary’s

VOIP2801(config)#ephone 3
VOIP2801(config-ephone)#description Mary’s Phone
VOIP2801(config-ephone)#mac-address <MAC Address>
VOIP2801(config-ephone)#type 7960
VOIP2801(config-ephone)#button 1:4 2:2