Restarting any Mitel/Aastra VoIP phone can be accomplished by removing and then restoring power. For some phones that receive power from the data port (referred to as having “power over ethernet” or POE), and therefore do not have a power brick, you can unplug the data port at the wall (or at the back of of the phone) to remove and restore power.
Note – If the message waiting indicator (MWI) light at the top right is turned on (the light is red and blinking), restarting the phone will turn it off. It your phone is rebooted for any reason, be sure to check your voicemail box periodically until the message waiting lights are automatically reset overnight.
MWI lights can be turned on manually as well, and prior to the routine overnight system reset, by contacting ITS Communication Technologies at telreq.unc.edu/telreq
To restart the Mitel/Aastra VoIP phone without having to remove power you can view the step by step instructions (which includes pictures) below. Be sure to select the document that pertains to your model phone.