how do you handle cutovers to new phone systems that are different than the old system. For example, moving from a 2 digit extension system to a 3 digit extension system. What do you say in the autoattendant to get callers familiar?

I removed a panasonic (2 digit extension) and installed a Norstar (3 digit extension). despite training sessions there has been ongoing confusion.

Looking for some advice suggestions or past experiences.