First verify that the extension you moved is in fact the extension number you think it is. Leave the handset in the cradle, and dial FEAT 99. If it's not a display phone (GASP!) call another extension to verify the number. The display will show what extension number the phone is, despite what the label may say. Next, call that extension from another phone. If the display of the calling phones says 'Invalid', that extension number isn't hooked up anywhere. Depending on your software version, an unplugged phone can show up as in DND, or will immediately forward to voicemail.

If you can call the extension normally, go to the phone (s) with blinking buttons, leave the handset in the cradle and dial FEAT, #, 9 then press the blinking button. The light should go out.

Sometimes the thoughts in my head get so bored, they go for a stroll through my mouth. This is rarely a good thing.