I just want to contribute that this line right here "BUT DON'T LET GO", enlightened the hell out of me.I kept getting to what I thought was the password to reset, but wasn't.I ran into a similar problem with some Polycom sets but it was much more gruesome because all of the authoritative details on the web didn't work.We had three Soundpoint IP 550s, one Soundpoint IP 331 and one Sound Station IP 5000.
However if you don't know the password, you have no choice but to do a factory reset to start using these phones on a new system.
Then wait a second or two until the cursor comes back before entering the next letter.
3) Switch back and forth between letter mode and numeric mode.
Literally continue holding it down until the screen changes automatically to a password screen.
Note that if you press the "Setup" button when the auto-boot screen pops up, it'll go to a password screen that looks identical but where every attempt to authenticate will fail.