Learn how to use the speed dial on your HTC One. Use Speed dial to call a phone number with a single tap. For example, if you assign a contacts number to the number 2 key, you can just press and hold 2 to dial the number.
Note: The number 1 key is generally reserved for your voicemail. Press and hold this key to call voicemail and retrieve your voicemail messages.
Note: You can also press and hold an unassigned key on the dialpad, and then tap Yes.