Like many people, I use a Zabbix system to monitor my servers. If there's a problem with one of my servers, Zabbix will send a message to the email address of my choosing. (Many - most? - monitoring systems work this way.)
When an alert happens, I'd like to have my phone wake me up with a loud sound. But I don't want it to make a loud sound at every email or SMS it receives.
Are other mechanisms available for reliably delivering alerts to mobile devices, which could be configured with a loud, annoying alert tone?
I've been playing with Pushover for sending Nagios alert push notifications to myself and other on-call staff. The Pushover service itself is free, until you start sending thousands of push notifications a month (hopefully for your sanity, that's not the case). Pushover can be configured with its own set of alerts, which you can make as annoying as you'd like. I'm sure there are many other push notification providers out there - I've just only had experience with Pushover, so that's the only one I can speak to with any authority.
The big issue with either SMS or email for notifications is that neither of them guarantee delivery within a reasonable amount of time. Email can (and does) frequently get hung up in various SMTP servers, and I've seen SMS delays on the order of weeks more frequently than I'm comfortable with.
With push notifications, there is a much stronger guarantee that the message will get pushed out to the user's device within seconds. In my testing with Pushover, the notifications always arrive in under 5 seconds after I hit their (very simple RESTful) API. There is always a possibility that your push notification provider's API is down, but you could always catch that condition in your notification script and fail back to email, SMS, or even something like PagerDuty (which provide a great service, IMHO).
There's a thread on the Zabbix forums about using Prowl to get push notifications to the iPhone:
https://www.zabbix.com/forum/showthread.php?t=20220
It links to this blog post:
http://blog.skinkers.com/2010/12/08/zabbix-push-notifications-for-iphone/
Prowl is an app for sending notifications to your phone:
http://www.prowlapp.com/
One tool for system alerts is Cloud Alert. While it was originally made for the banking industry, it does have the loud configurable ringtone you require, and a command-line for integration with scripts. (Disclosure: I work for Cloud Alert)