English has no formal and informal forms, and thus the degree of formality when addressing somebody is often conveyed by the use of the first name. As the line between Mr. Smith and William is not clear-cut as in French, German or Italian, people are often more relaxed in using first names.

Do not try to call a Swiss by his or her first name unless you are invited to or know this person very well. Although the person you are talking to might understand that your intention is to be friendly but not impolite, it will probably cause some discomfort nonetheless.