Heart attack GPS cellphone

We are Internet and cell phone novices, and are writing you in desperation because our father has a severe heart condition which can cause a sudden heart attack at any time. He is otherwise in fair health, and can walk, go places, etc. On the cardiologist's advice we have purchased a portable defibrillator to use which we carry around when we go out with him.  At home he wears a LifeAlert pendant which he can press to activate the system operator who has been instructed to call 911 for a heart attack condition if our father is unable to speak to the LifeAlert operator.

However, outside the house he needs a cell phone in which if he were having a heart attack, and were sufficiently conscious, he could quickly press a dedicated 911 button, and a phone which would have GPS enabled so that his location could be determined if he were able to say heart attack into the phone as he was falling to the ground, for example.

We have gone to Best Buy and other cell phone centers, and upon their advice purchased a Verizon Koop flip phone with a dedicated 911 button. Unfortunately, we now realize this is not a good choice because in order for our father to use it, he would have to take the phone off of his belt, which is not easy because the clasp is tight, probably necessarily; turn it right side up; flip it open, and then dial 911. The nature of the heart attack might be such that he would not be able to do this. Do you have any suggestions for a phone in which a dedicated 911 button is available without having to flip it open; with GPS; and in which he could simply push a dedicated 911 button if he were falling to the ground? We asked also about whether there are any voice command type phones, but were told that all of existing cell phones, including those with voice command, require that one press one button, then wait several seconds, and then press or do something else. We are hoping that there is something more immediate in which he could have the phone set up ahead of time; have it easily accessible on his belt or around his neck; and then simply press a dedicated 911 button, or yell into the phone 911, heart attack, and that the GPS would allow his location to be determined if he had lost consciousness.  Thank you very much for your assistance.