I wonder how many drone smuggling attempts have succeeded. I'm a drone hobbyist, and I don't think it would be at all difficult to deliver small packages with a very low chance of getting caught.
Wouldn't some kind of ballistic launcher, maybe with a parachute, be easier? Not so much for cellphones, but for light, robust items like cigarettes, dime bags, etc. You could probably do it with a slingshot.
I think your range would be much lower with any practical ballistic launcher, which makes it easier to get caught.