Good habit. Introduce yourself and advise you have a speech impediment at the beginning of the interview. Look them in the eye, offer it with your introduction and say "so just be patient with me if need be... I get there." Smile and mean it. Own it. It puts you at ease with disclosure and informs them of the situation. Never ever ever say sorry for it. In any context. But do educate those you fear speaking to. Run towards those fires. Peace.