When talking on the phone, "You are breaking up." is the same as "Your voice is breaking up." Next, "It's difficult to imitate a British accent" is the same as "It's difficult to copy a British accent." and both are correct, but notice the addition of "a" before "British." Lastly, I think imitate is a better word to use than copy, but I'm American. Maybe a Brit will have a different answer ;)