Last time I checked, which was awhile ago, Blackberry was the only non-pager that could guarantee delivery within a known time-frame. You can't run server alerts over SMS, since it might take an hour (I've heard of a 12 hour delay around New Year's), or it might not be delivered at all.
Seems like there might be a market here for an app which acknowledged receipt and publication of a message to the target's phone, coupled with a service which escalated to a phone call to the target if it times out waiting for the acknowledgement.
I think the guarantee is the tough part; you have to own the hardware and have at least some control over the infrastructure.
Anyway, I find Georgie's comment fascinating. Sounds like there's a way to guarantee SMS delivery, though. From Wikipedia on SMS/SS7[1]:
> Therefore, it is possible to avoid delays and message losses, offering full delivery guarantees of messages and optimized routing. This model is particularly efficient when used in mission-critical messaging and SMS used in corporate communications.
