While this is about the best size for a phone, I want to point out that making a device for the user and maximizing corporate profit seem to be incompatible goals.
Smartphones are no exception in this - the vendors are mostly interested in making not-the-best phone that'll only last a couple of years so that they can then sell you another one and profit.
Smartphones are no exception in this - the vendors are mostly interested in making not-the-best phone that'll only last a couple of years so that they can then sell you another one and profit.