I always wonder how actors manage to make those phone scenes believable. I mean in reality there is really no one on the other end of the conversation, but they have to make us believe that they're really having a conversation or a conflict. We as the audience of course can often see the two sides of the conversation, but the actor is either alone with the phone prop, or having someone off camera reading the other person's lines, or if they're very lucky the actor on the other side of the call is standing behind the camera doing their part of the conversation. But still, has to be difficult to make it believable.
I think Richard Armitage has had more than his share of scenes when he's talking on the phone and having to do some quite emotional scenes. I think he's amazingly good at making us believe this conversation or confrontation is truly happening. You can see how his eyes especially change depending on how the conversation unfolds, and make us believe he's listening to what the characters on the other end have to say for the very first time. He also manages to do it in character and to look quite good when he does.
While looking through photos and caps of RA on the phone I was happy to find several of him talking on land lines. There's a lack of mobility for the actor when tied to a phone on a desk or a table. But again he manages not only to make the conversation believable, but also to give the sense of the character and the emotion of the moment.
*screencaps thanks to RichardArmitageNet.com and RichardArmitageOnline