Set Shared Line for One Button Access
See the below for the steps to get it set up.
Make the following setting change to your Shared Line voice mailbox and your users can access the mailbox by simply pressing the key programmed with that Shared Line mailbox key.
Once you open up the Shared Line with the mailbox attached, set the AutoDial option to Voice Mail, the field next to the arrow will auto fill. Save it, and those with that mailbox on their phone will be able to access the Shared Mailbox, by just pressing that key.