We told my DHs family via phone as they live a fair distance away. And we told my family in person mainly. Everyone else was whenever I was talking to them next. I did send a photo frame to my Grandparents with a note inside saying 'Reserved for baby due 28th Sept' I got that idea from one of the great ladies on this site.
You could try maybe sending a baby balloon out or invite people over and have a balloon on the letter box.