Depending on the voice mail system you are calling you can use either pauses or waits in the dialing sequence. mine is set to dial like this;
13065551234pppPASSWORD#pp1. each small p is a 2 second pause so when I hit the speed dial I don't have to touch another key and it will take me right to the first unheard message. You can set up any speed dial this way just create an address book entry called "Office Voicemail" get your dialing dequence setup and then set it as a speed dial number. It might take a couple of tries to get the pause sequence figured out but when you do it should work fine. If you use the w (Wait) command you have to press another key to initiate the next set of numbers each time, sometimes this will work better depending on your voicemail system.