The Intuity is the standard voice mail for Avaya, but of course u have smooth operator. There is nothing in the Definity that I know of to change the output of the voice cards to avoid voice cutoff.
And I am not familiar with SMooth operator. Sorry.
Sometimes there is voice cutoff with cell phones calling in due to static.
About the only thing else that I know u can do, other than finding in the Smooth operator where to change the db level, is to do "change station xxx" for each of the analog ports in the Definity, and change the "rotary digits" to "no". This will make any static on a call not be mistaken as a rotary digit or switch hook flash.