Emergency sms to group of mobile phone users

Dear Tech Republic users. I’m just wondering what the easiest and most reliable way is of setting up an emergency sms text message distribution service to getting a message to a group of mobile users. I know this can be done through for example Outlook, but what if the email line is down. This would presumably have to be done via a mobile device?? No doubt the latest IP phone systems can do this, but failing an upgrade what do you suggest. Just for the reference all our users are on 1 mobile network. Hope you can help.