I had this discussion concerning Luke, Vader and Leia using telepathy during Empire Strikes Back a few times before.  I don't know if they actually did.  When Vader says, "Luke.  Come to me.", for all we know Luke only feels a yearning, a desire and knows it comes from his father.

Also, when Luke calls out to Leia he simply calls out, "Hear me...".  It's not like he says, "Hey Leia, I'm hanging from a weather vane beneath the city and could use some help!".   I figure Leia just feels pain, since Luke is in a helluva lot of pain, despair, and a great deal of convoluted emotions from over that-a-ways.  After all, she and Landon still had to look around and Lando was shocked when he finally spotted the poor Jedi clinging to the weathervane.

Mind you, by the same token, I could be completely wrong.  It's very open to interpretation.

In my opinion, the force which exists between all things, carries the emotion or the feeling through itself but the Force isn't sapient.  It's like talking to a cat or a dog.  Words generally don't make sense to an animal.  Sure they may come to understand a rare few but cats and dogs understand emotions, basic impulses better.  Since your transportation medium has no concept of language, you can only send what it in terms it understands.  If Anakin tries to get the force to "Tell Obi-wan there is danger", the force doesn't understand but a feeling of fear and alarm to the one that is close to Anakin like a brother is something it may understand.  This would make the close friends, relations aspect of the "telepathy" make more sense.