sorry critter, I gave a very simple answer to your question...maybe this will break it down a little more....when you are out in public you can pick up on ppls feelings around you , but it can sometimes be hard to really know who or what you are feeling exactly. so you just feel it and let it go,( that's the hard part for a lot of empaths to do) but when you get a text, phone call etc... it is usually from ppl you know and have a connection with. so you probably already know if something is out of whack or wrong with them, ppl you have that relationship with, friends, family, even aquaintences you see regularly are very easy to feel....so its not felt because of the text or call, but usually verified by the text or call....if that makes sence???
even on bourds such as this, when someone comes in and writes/responds they are leaving a bit of their energy here, and depending on what they are projecting, that can be felt as well....especially if they are actually trying to put forth a block or "shield"......as far as what do you get. it is usually emotion, esp strong anger or depression comes through the strongest, you will actually feel what ever emotion they are feeling, so much so its sometimes hard to not know its not your own.....as you progress you will learn to ignore or release the white noise, everyday chatter so to speak, and just pick up on what you want, you can then go out, breathe in all the energy and release it without going nuts....lol...that is actually a good exercise to do regularly just to control that ability....explaining empath abilities and feelings can get confusing and long, but maybe that helps a little.....