PhoneTop.com, they won numerous awards from Cisco IP telephony users group. Very attractively priced as well. With PhoneTop Messenger you can do:
Text messages to phones and email groups
Audio paging to phone groups
Push surveys and Amber alerts
Soon you will be able to push alerts issues by National Weather Service -- pushed to phone groups...
PhoneTop Alers pushes out EAS alerts to phone and email groups -- EAS stands for US Emergency Alerts System, which uses FM/AM radio to broadcast emergency notifications to general public based on geographic areas.
PhoneTop K-12 allows teachers to take attendance on IP phones.