on the stock dialer, use the keypad. at bottom of screen is icon for voicemail. press that, it brings up a list of your voicemail. think this is closer to what op is looking for. long press 1 dials your voicemail.
I am on Verizon so not sure if carrier specific. Good luck. Sorry if this 8s no help. Rereading your post, have feeling t mobile deleted this or it was always vzw specific.