Can an astrally perceiving magician hear his commlink earbeads?

Percieving, yes. You're still aware of the regular world as well as the astral.

Projecting, no.

Do you have a page reference for that?

No page reference, but you can. You can drive a car or fire a gun at -2 while Perceiving (SR4 pg 182), so I don't see why you couldn't hear a non-Astral noice, even if it required a Perception test.

I don't have my own page reference at the moment, but I think SM says that communication on the astral is more about emotional content than hard information. In previous editions, astrally projecting and perceiving magicians could hear face-to-face speech just fine, because they were communicating with a living being. But any noise coming out of a machine tended to sound like Charlie Brown's teacher, because the machine isn't a living being.

And commlink earbuds are machines.

My understanding of Projecting was that you were essentially seperate of your body, asides from getting very intense stimuli like pain signals from it. The logical read on that would be that hearing your commlink is something you're missing out on.

You can talk to people while astrally projecting if you Manifest. That's where an astral form displays itself as a kind of ghostlike image on the material plane. You can also hear physical sounds, etc while manifesting, it isn't just about whether you're talking to a living being or not. But your earbuds are going into your physical ears, and when you're astrally projecting you are not in your body, so you can't use its senses.

The ways to communicate with the material plane while astrally projecting are a) manifest, b) send a spirit to be a messenger back and forth, or c) use a Mind Link or Mind Net spell.

I've always just thought of perceiving as adding an extra sense. I usually describe it visually to the players, but you should be able to use your other senses with said penalties.

I agree.

Think of astrally perceiving as a mage's equivalent of a hacker's augmented reality: you see and hear more things than you normally can, but you still see and hear everything else that you normally can.