1) Unplug the phone
2) Hold "7" button
3) Plug in phone, continuing to hold the "7" button until the display says "CONFIG TELEWORKER", then press "*" for Yes
4) At the "DELETE/NEW SETTINGS?" prompt, press "#" for New
5) At the "IP ADDRESS TYPE:" prompt, press "*" for IPV4
6) At the "TELEWORKER GATEWAY:" prompt, enter the IP address of the Mitel server. For example, if it is 192.168.10.10, enter "192168010010" or "19216810#10#". STAR is backup, # is "." if less than 3 digits in the octet.
7) Press "VOL DN" button
8 ) At "STORE CHANGES?" prompt, select "*" for YES
The phone should reboot and come online.
This process will cause the phone to ignore any Mitel specific options (which appear to not be setup) and contact the system directly after getting base DHCP information.