Impossible, no, impractical most defiantly!
The way I see drone delivery service becoming feasible is if these companies use drones, or what in reality would be a automated transport helicopter to deliver a large quantity of goods to predefined locations where said goods are then given to human couriers to final delivery to customers.
The idea that we would have direct to customer drone delivery is extremely impractical because of the amount of drones needed. Let us take the annual iPhone release date. An iPhone is small enough to be delivered by drone, and is not an item that will be replaced by streaming, or digital delivery, such as a BluRay or video game.
Take San Francisco, or any major city, how many people pre-order the iPhone for day one delivery? A few hundred, a few thousand? Lets say 3,000 people in the bay area pre-order their iPhone for day one delivery. How many drones would it take to make all of those deliveries on time? How many in the air at the same time? 200? 500? And that is just for the iPhone. Now add all of the other orders that have to be fulfilled that day. How many drones are in the air at once? There will have to be a limit, otherwise the sky will be filled with drones. From Amazon, UPS, FedEx, local couriers, etc... With said limits in place does it become feasible to even run such a delivery service?
How will security be handled? Everyone knows iPhone release day, or PS4 release day, or Xbox, etc... Take out the drone as it is flying, could the police even keep up with the amount of theft that would happen? Rural delivery makes a little more sense, but makes it even harder to control security. Drone gets taken down en route out in a field, the drone, and it's cargo could be taken long before any one arrives.
The only way I see this making any sense is as I stated before, large automated transport choppers, dropping of large quantities of cargo in per-defined destinations for local human delivery. Drone drops off cargo, goes back to warehouse, comes back with another load just as local delivery returns from making previous deliveries.
Direct drone to customer delivery, not for a LONG time, if ever!