Though the discussion went on some time ago, I thought I would add one more possibility to consider.
As an alternative you can also consider using hardware sms gateway. This a kind of device which you buy, put inside a SIM card from your carrier, and connect to LAN. It will send your sms alerts directly to a GSM network. So, your'e independent from your internet connection. Hardware sms gateways are devices that are embedded computers with built-in GSM-modem. They usually operate on Linux, have built-in database and a web server.
Advantages of this approach is surely reliability and less pain with integration. But there are disadvantages too: this costs you money. You'll have to make one time investment in such a device.
Just and example of such hardware sms gateways would be SMSEagle
Here you can get Zenoss plugin for this one.