All of mine have been born at reasonable times (3pm, 10am, 6pm and midday) so we tend to call our parents straight away and let them tell the extended family. We then text friends.

If the next one comes in the middle of the night we wont tell anyone until at least 7am. I'm pretty polite and believe in letting people sleep - but maybe that's because I've not had a full nights sleep in over 6 years and I really respect sleep LOL