How did you come to know that both FOM and cantonal authorities approved your permit?
Had you called them and the news was told to you verbally?
Usually (Well at least in my case) you get a letter with in a week or two (maximum) with your details, type of permit and by when should you enter Switzerland (If you dont enter with in given time your visa will no more be valid).
You cannot start work with out that letter. Hope by now you have received the letter as i see your reply is 4 days old.
Wish you good start and have good time.