It was big news when Sprint announced last week that it would offer a $69 package on cellphone service, including unlimited calling to any other cellphone, unlimited texting, some fun bells and whistles like GPS navigation, and most important: unlimited data. Lots of people were celebrating the move, with writers and readers pondering switching providers to Sprint. As a former Sprint customer, I’m not in any hurry to get back to the company with the worst customer support I’ve ever encountered (in any industry). But then I look at my iPhone plan with AT&T, which squeezes an extra $20 out of me for unlimited text messaging, and I wonder…

To keep people like me from jumping ship, the other big providers will inevitably respond with similar plans. This could be a great development for consumers — a good old price war! Taking it a step further, though, it could be a good thing for mobile/cellphone tech in general: Since data service is so cheap now, primitive phones will fall into the bin of obsolescence. Soon, pretty much every cellphone will be a smartphone.

As smartphones spread, though, Sprint’s big move might have an unexpected consequence: Putting itself and its fellow providers in a weaker position. My reasoning after the jump.