You can use a button programed as a Station Speed Dial with a dial string of “[V-Mail ext number]*[Ext number][password]#1 (for example, if the voice mail is ext 276, the extension is 104, and the password is 1234 then the dial string would be “276*1041234#1”  that would give you one button dialing into the mailbox and start playing the first message. 
Of coarse, you can leave off the password, the #, and the 1 if you want to be secure. 
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