You make it sound like it would be prohibitively expensive to add a cellular antenna to something. A DSi today costs $150 on which they presumably make a profit

You make it sound like it would be prohibitively expensive to add a cellular antenna to something. A DSi today costs $150 on which they presumably make a profit. Cell phones typically cost $200 and come with hundreds in carrier subsidies. If you bought one straight up it would cost $400 to $600. Considering Nintendo makes money on $150, they could increase the cost to $250 to add "all those features" and the DS phone would still be free up front after carrier subsidies. I'm not sure what business you think cell phones makers are in. They only make money by selling hardware so of course each unit needs to be profitable.