If you're traveling over the speed of sound with some companions...can you talk to them and can they hear you?

yes.. or no... and why... scientific terms are good.

Yes they can hear you because the air around you goes the same speed. of course if you would be shouting out the window at your friends on the ground they could not hear you.

All things being equal, yes a passenger in a jet traveling at the speed of sound can talk to his captain or speak to others over the telephone on the ground.
If you were outside the plane and could move your body that fast (such as when all students leave English class on friday afternoon) you could still hear others perfectly fine,
even under the conditions described above. Traveling at the speed of light, now that raises some real interesting challenges.....
Scientific terms are like a language that is universally recognized as valid, if we see, hear, smell, can touch or visibly prove something is there it becomes a scientific fact, a rational proof of understanding. We can measure Darwins theory, can't measure that other thing they are trying to push off as science which is faith based and irrational. It could be true but evidence
scientifically doesnt support it..and there is a large argument for the irrational in man(and especially woman), Kidding. But can you see how chaotic it would be if everyone had their own system of science?

Of course you can talk to them and they can hear you...they are traveling with you. They too are traveling at the speed of sound. Whatever external forces are at work around your group, you are all in it together.