Voicemail can do all of those, including the spam.
It's hard to "glance" at a voice system. However, you can get that same info out of a voicemail system too, if you desire.
You can't usually start in the middle, but you can still get the list in chronological order without listening to any of the message content, if you so desire.
Then your voice mail system is stuck in the stone age. Even my cell phone's voice mail system tells me the number, if I ask for it.
My cell phone's voicemail can both reply to voicemail (if the caller uses the same system), or automatically connect me to the caller's phone number.
This is tougher, mainly because it would be very difficult to interact with a voice mail system due to the lack of interface.
It might be faster for the sender speak it, but it's a hell of a lot faster for a recipient to read text then listen to you stumble through a message, repeating parts, fading out because you're in a noisy or windy location on your $5 cell phone or because *I* happen to be in a noisy place.
Voicemail is for the convenience of the sender, email is for the convenience of the recipient.
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