Guests will often ask "What is our extension?" They don't get the extension is the 6 to 7 digits at the end of the URL invitation. Can we add any clarity to the email invitation? See below for edits in red.
Also, I like the idea of cleaning up the extra commentary in the email invitation. Keep it simple and that will speak to Lifesize's ease-of-use.
Adding more information about calling from an existing Lifesize system seems to make things more confusing or distracting from the basic purpose - to get the guest on the call without picking up the phone to walk them through it.
You're invited to call [Name / VMR] on Lifesize.
Connect over video, our extension is: 123456
Call in by phone, our extension is: 123456
US: +1-844-572-5683 extension 123456
Try it free at www.lifesize.com.