Hmmm. This is an interesting idea. From a practical point of view I don't know that it would make a difference in most cases (at least not in the field).
In the grand scheme of things, medical history really doesn't matter. If you've got a patient who is ill enough that they are unable to answer you, you probably don't care all that much what their medical history is. You're too busy treating the current problem to worry about it. The same thing goes for consent. I don't know how things work in the UK, but we have a lovely thing called implied consent. If you aren't over the age of 18 or aren't CAOx4 (conscious alert & oriented to yourself, location, time and problem) we get to make decisions for you. If you are alert your emergency contact friend doesn't have the right to decide for you anyway.
I personally would never call a number from a patient's cell phone. It's the job of the emergency room or of the police around here to notify NOK. Before agreeing to be an emergency contact, people should also consider the implications of making health care decisions for someone who has living family. In the US if you aren't a health care proxy it can be a dangerous situation and you can open yourself and the healthcare provider up to serious legal issues. (think about Teri Shaivo) I would never listen to care instructions give by some dude over the phone. Who knows, it could just be some stranger you met in a bar named Ice.
I'm not discouraging folks from doing this. It might be helpful for the emergency room if they need to notify someone of your injury/death. However, I don't think it is going to save many lives. If you are really looking to be helpful, keep a card in your wallet with your name, DOB, medical history, medications and drug allergies. I think most prehospital providers would be more comfortable looking there than calling a stranger on the phone.
