If you enter your carrier's voicemail number in the voicemail setting of your phone app you should be able to dial direct by long-pressing the "1" button on the phone app's keypad - at least that's how it works on most phones. You may be able to call directly by clicking on the voicemail notification.
It may already be set up. If the "1" key has the voicemail symbol printed on it, give it a go. If it doesn't work, go into settings and enter the number. If you don't know the number, your carrier can give you it.