You have one body. Two arms, two legs, a mouth, two eyes, two ears, a nose, lungs, a heart, a stomach, all physically connected to the same nervous system. Your nerves aren't wireless. Your body is one whole thing, and it can't be separated and made to occupy multiple places without harming you. So you can't be in two places at once.
Or can you?
To occupy a place is to be able to interact with it. I first encountered this view in discussions of God's omnipresence. It is a solution to the problem of how God can be entirely everywhere. Not some part of him everywhere, as a distributed body, nor all of him multiplied so as to be reproduced everywhere, but him, entire and complete, at every place. The solution is to suggest that God's omnipresence is his ability to know what is going on everywhere and to respond to it from anywhere and everywhere. His actions and knowledge are not bounded by space, and this makes him omnipresent.
So, if I were to be in two places at once, I would need to be able to perceive both places and perform actions in both places--at once.
The biggest problem we face in doing this at this point is that it involves multitasking, which we can't technically do. What we actually do is switch back and forth between tasks very rapidly. Let's ignore this problem for the time being, because we get close enough.
When you are talking on the phone, your ears and voice can reach two different, and usually distant, locations. You can usually still hear what is going on around your body, but you can also hear what is going on where you are calling. Two locations become linked by your phone. That is just the most common way it works, of course: there is pretty high demand for technologies that will let you be in two places at once now. That is what allows for telecommuting: your presence is no longer limited to the geographical space around your body.
It gets weirder.
Massively Multiplayer Online Games create a new, shared space which many people can occupy. You occupy both your desk, and this artificial world. The feature which makes it most obviously a world is that multiple persons can communicate in it and about it, and can get results relative to it, and all this can happen within its space. So within these games a person can occupy, not only two places, but two distinct, though connected, worlds.
You are still limited, though. You can't fix a sandwich and work at the office at once. Pretty much all our devices for telecommuting involve our fingers, and, even if they didn't, it would hard to multitask so thoroughly.
And this is just descriptive. I haven't even started thinking about the ethics of this.
I want to say we should avoid multitasking, and that we should be present wherever we happen to be. That needs some nuancing, however, especially seeing that we can't really function in this era without phones.