What you need to know about emergency notification systems:
Prices range from $1 to $10 per user (message recipient) per year, depending on the feature set of the software you select. The larger the number of users, the better the deal.
Don't fall for the bells and whistles. Focus on core functionality. Who is your population, are they domestic or global, and which contact mechanism will work best for them? If you need a global system, make sure the software can support variable-length phone numbers, for instance.
Test each system thoroughly. Make sure this will really work when you need it the most -- take your time, experts advise.
Establish guidelines and procedures right away. How the system will be used, and who is authorized to use it and for what, are critical decisions. Make sure the interface is appropriate for the users involved.
Don't overuse it. Although it may be tempting to send alerts to, say, make sure employees turn in their timecards, you don't want people to start ignoring these messages. Make sure it's saved for emergencies.