How to remove static IP from Mitel 5312 and enable DHCP
hold the 2 arrow keys(up/down) keep the up key and pres 2 3 4 after that you come in the configuration scroll with the # to modify static value and press 0 ...
A guess, to be fair, but what happens if you remove the MAC address of the telephone device from the extension number details (User Configuration I think) in the 3300 system admin tools, so that the phone has to be registered again prior to use? This won't delete the telephone number/user, just the association between their number and that device.