Awesome from a tech point of view, clearly ridiculous from an EMS/everything else point of view.
This particular app aside, I can see some sort of iPhone magic being useful for getting AEDs to the arhythmically challenged with a tad more haste.
The biggest problem I see with public access AEDs is that by the time somebody remembers it, goes and gets it, has to find the key to the first aid room, comes back, trips over, and fumbles about with the AED, the coroner is ready to release their findings on the death.
Still, I don't see how iPhones could achieve more that what a couple of security/staff could do with their radios. Additionally, they could probably do it without their radio's freezing and asking if they want to upgrade to the identical radio 2.0. <_<
'Course, if it was a Windows phone, you'd get an annoying message saying, " You seem to be attempting a resuscitation, would you like to know the location of #req%-serv//Steakhouses?"