It's good for the bosses. Firstly no written contracts or liabilities in the books. Hence, costs presented by employees are a direct operational expenditure. Also, they tend to pay you less than what you've spent...on their behalf.
It's been working like that for ages here in Europe. No brainer.
Now, the major corporations that want to control your life via a phone will supply you, usually a cheap BB 8520 or a Nokia and then the IT's run circles around you. The costs obviously are paid by the corporations, but then they do fix a limit for calls. Over that and they are into your pocket, or should I say, into your salary.
Unless you're forced into that as part of your job tools, nobody buys into their schemes. Or try not to. The Labor Unions have a whole manual on this...much less BYOD stuff. What? My phone and they control it? Forget it.
So in the end, the only come-short character in this story is always you, the employee.
BYOD - nope, thank-you!
Much the same in the EU with company cars. They pay you a supplement on your salary and you provide the car. Yikes. No thank-you.
Unfortunately, a lot of unemployed are falling into these traps because of the need they have.
Like vultures the bosses grab any morsel of profit they can.