But you can't make a speed dial button on the Intercom, which is where you are dialing into the voice mail system.
At home, I looped an extension to a line port, took all lines away from the extension, took the "line" out of the Auto Line Select, and set up a speed dial button to dial 777p10#XXXX#pp2p0.
Now I press the "line", which pulls intercom dial tone, press the speed dial button. It dials VM, waits, logs me in, plays the number of messages, dials 2 to get messages, plays the header, then plays the message body. Set up additional buttons to delete and save, and it makes to easy for family members to use voice mail like an answering machine.