Accent can give your talk a real boost as they are unique and can sound very atttractive. Donot waffle or attack the client. Stop to breathe. Pausing is very important. And a little colour to your voice.
Expressions are very important.
Relax when you are talking. Imagine you were talking to your friend. Your attitude is expressed by the way you talk over the phone. Don't rush the call and use your sales techniques. Remain professional and smile.