If people were willing and able to fly, the free market would close this arbitrage by ... driving up the cost of flying to Dubai. The other prices are controlled.
The article assumes you will not be paying the import duty charged in India i.e. you're bringing an open box/you own the iPhone you bring from Dubai. If you were to start a business bringing in phones in bulk you would have to pay the import duty after transportation and logistics cost which would leave a negligible margin for you. It can only be viable if you choose not to pay the import duty in which case it's smuggling (if you're bringing in with intention to sell).
people flying to dubai on different days across different flights to buy a couple iphones for themselves, or even as speculators, would not make a big enough dent
Apple will more likely correct the pricing discrepancy to sell more iphones in India themselves
