Not a system I have done a lot of work on.

Have all the extensions gone back as they were, including the original phones?  His extension gone back to him (100) with HIS own phone?  Key programming could be in different places on different extensions.  you may be pressing VM, but actually pressing a key progammed for something else?

LG systems do only use one pair for the digital extensions (and only one pair if using SLT phones, but from a different card).

The extensions key programming etc is stored in the system, so if he has used someone elses phone, and they had the VM key programmed to a different button, his phone would not work as expected (if you see what I mean).

I assume the VM key is just a standard programmable key?  One of the LED keys on the these phones?

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Can't reallyt think of anything else that would disrupt the operation if not programming changes have been made, and everything has just been physical moved.  Not sure if the line not being live could perhaps affect it