Shortly after my group got switched over to new fancy-dancy IP phones, one of my colleagues sent me email to say "This morning, when I picked up the phone, I kept getting a 'URL not allowed' error. I fixed it by rebooting my phone."
So this is what the world has come to.
Bonus chatter: As many readers surmised, these "new" IP phones arrived over a year ago. On the other hand, I never did get to learn all the features of the device before it was replaced with a different model of IP phone. Progress.