Hi A. - I was an only child also, and I remember feeling like "I don't have any friends".
Now I have 3 children, they fuss and fight between themselves, 2 girls and 1 boy. Boys are just completely different from girls. Firstly they mature much more slowly than girls and secondly I think they learn differently too.
My oldest daughter, 11, complains ALL THE TIME about not having ANY friends! Talk about drama queen honey - she has the Oscars all sewn up.
At first I was patient, I listened, I hugged, I sympathized, I offered advice........ now I am to the point that I have said it all over and over and over.
She has a problem with being bossy and wants to be in control of every game. I have told her to chill and try to let the others express their ideas, they might be fantastic at something and teach her a thing or two.
With the interupting thing - OMG been there. If I am having a conversation (or on the phone) and they start calling me from another room as they are walking towards me - I turn my back to them first, continue my chat, the next time they butt in - I show them the shush finger on the mouth, continue chatting - the next time I put my hand over their mouth and give them the "mommy look" of go away before I melt you in the microwave or some other obscure thought.
What ever you do- "DO NOT SPEAK to them" and do not get visably angry. Be in control - do not let them work you.
Now, when my kids do it the first time, all I do is raise my index finger and they immediately clasp their mouths and say sorry. They understand that I will answer them as soon as I am done talking to the other person. When done, I go and find them and ask them what they need then.
I hope it helps, just don't let him get away with it because you are not doing him any favors in the long run. As he grows into an adult do you want him to succeed and blossom and become a great, kind and respectful man? We as parents have to teach our children "Life Skills" or some one else will and it will not be good.
God Bless
M. F