The effect of changing a LineURI on Lync Phone Edition Phones

We have a lot of CX500 phones that have been authenticated on the internal network using PIN authentication, and then sent out for use externally. Today I had a requirement to change the LineURI for a few of them, and was worried that in doing so the phones would be disconnected and need to return to the office to re-authenticate.

To test the theory:

1. I grabbed a CX500 and logged in as a test user. 
2. Once logged in I moved the phone to an external network
3. I then changed the LineURI and waited 10 minutes
4. The phone number had still not updated on the phones display so I rebooted the phone
5. Still the phone number had not updated on the phones display, but good news I logged in OK
6. I made an inbound call to the newly assigned number and it worked, so I assumed the display number may just take some time to filter through
7. After a few hours the display number on the phone finally updated. Running update-csaddressbook did not seem to accelerate the process
8. Days later the phone is still signed in with no issues reported