Otherwise, with a phone online, do the following:
Press both the up and down arrows sat the same time. Release the top arrow, but continue to hold the bottom one. Press the the 2 key, then the 3 key, then the 4 key (spelling out cfg). You can now release all the keys, and the display should give you the phone's menu.
If you press * or #, go into the network settings, view current, and then using the down arrow, page down through the information. One of the options should be ICP 1. This is your controller's ip address. Continue to page down till it give you an option to press * to exit. Again hit the down arrow until you get the option to hit * a second time. It should return the phone to date and time.
Couple of warnings. If the phone is a 5220, its an older phone, and I'm not sure this will even be possible. Second, not sure what will happen if the phone rings while your doing all this.