Its Simple! You create a group, add or invite people into your group, then record your message. Ennouncement will then call everyone in the group, and as soon as they say hello or their voicemail message stops playing, it will play back your message.
"Soccer practice is canceled today due to weather conditions. Next practice will be Wednesday at 6:00pm. See you all there!"
"Good morning, today’s meeting at 12:00pm has been changed to 3:00pm. Sorry for the short notice. I hope to see you all there."
"It’s A Girl! Kate was born this morning at 8:46am weighing 7 pounds and 3 ounces. Come visit us at the hospital tomorrow!"