Unfortunately, the carriers didn't adopt the same keystroke, so it's different by carrier, so it devolves upon you to learn the keystroke for the person you're calling. I didn't say these were going to be perfect.
Leave it to phone companies to do something complicated.
Here’s a guide to the different carrier’s voicemail-instruction-skipping keystroke.
In the event that you have a smaller carrier, the pound key seems to be a pretty common multi-use button, so mash away.
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