Dual SIM Card Phones? What is the strategy for operators/carriers

Over half of mobile phone owners in Europe have two or more phone subscriptions. Same is true of many advanced Asia-Pacific countries from Hong Kong, Taiwan and Singapore to Australia. So too in advanced parts of the Middle East from the UAE to Israel. In Russia more than half of phone owners have two or more phone subscriptions. Even laggard mobile telecoms markets like the USA are starting to see this, with about a quarter of American cellphone users having two accounts or more (think of a Blackberry user with a company phone, also having a private iPhone).