At launch, an unsubsidized 32GB iPhone 4 cost $599, let's be pessimistic and say you get two years of use out of it and are unable to sell it for anything, that's $25/month. Not exactly an extravagant business expense.
There is no way this is common and if it is, must only be common to iPhones.
I remember reading a thread on r/Android about smartphone use in Korea and someone mentioned people tend to carry around an extra battery when their main battery runs out. I presume Samsung dominates the market over there and their phones have removable batteries.