I see way more downsides to this than up.
There might be some utility to it, if it were ALSO a phone. And if it were a smart phone with a "smart gun" in it, you MIGHT get the anti's to give it a pass, if not actually approve.
On the other hand, once word is on the street that a phone might be a gun, I think you will see an increase in both the number of, and violence of attacks to get the gunphone by the badguys.
And, as mentioned, cops will be "at risk" from every person they see with a smart phone, and some of them are going to shoot.
Neat idea, for James Bond, or the Man from UNCLE, for the rest of us, not so much, I'm thinking.