Hate to say "I told ya' so" - but I did.
I saw a news article this morning about how some people in Eugene, OR did not receive a call from the county's emergency notification system about a tense situation on the streets outside their homes because the calls only went to land lines - not cell phones, and (despite them not mentioning this in the article) not VoIP phones either (e.g., Vonage).
Land lines are disappearing rapidly and there is currently no way for emergency notification systems to send messages to anything BUT land lines...unless of course residences and businesses are provided with a method of "opting in" to receive alerts by providing their community with their cell or VoIP phone number. And some communities do this, like the University of Oregon campus as mentioned in the video portion of the article I mention above.
But that solution has it's challenges, too. First of all, you have to educate people about the ability to register their other phone numbers. Then, what happens if/when they change their number and that number is reassigned to someone else who doesn't live in the same area? You have to assume that the registrant is going to forget they registered and thus forget to un-register. So now you have a bunch of bogus numbers you are trying to notify that clog a taxed cellular network even further. And based on various studies I have seen, chances are the messages won't get delivered to most of the cell phones anyway...
And just because my mobile phone is now associated with the location of my house, I could easily be somewhere else when a situation arises. Not that I wouldn't want to be notified that something was happening in my backyard...in fact, it might be helpful to know that there is a guy with a gun running around my neighborhood even if I am not home. Perhaps I am on my way home, and thus need to know that it's probably not a good idea for me to turn into my subdivision. If the EN system only calls my house line, I'm not going to know about it until I get home. This, in fact, happened to me last year.
And this brings up another point about location. I may be interested in receiving alerts about emergency incidents in more locations than just where my house is located. I want to know if something critical is going on around my child's school, my elderly aunt's home, my workplace, my route to work, etc. Now you're talking about needing a very complex system that can manage multiple phone numbers associated with multiple locations that I doubt taxpayers will want to pay for since they already gripe about fees for basic 9-1-1 service.
Regretfully, I don't have a solution. But it does bother me slightly every time I hear about some town purchasing an emergency notification system.

