Get an .mp3 file saying "Peter" or "Peter is calling you" or whatever you like (or record one). (I have "your daughter is calling you", "your brother is calling you", "your wife is calling you" [for the house number] and "your wife is calling you on her cellphone", so if I miss the call I know which phone to call her back on.) Put the file into your Ringtones folder. Go to Peter in Contacts, edit (depending on which Contacts app you're using, you may have to tap "More fields") and add that ringtone to Peter. Save.