Don't know if the smartphone prices are actually falling (apart from the obsolete models, of course)
But that is exactly the whole point !! Why would you buy an i-phone 6 TODAY, when you can buy that SAME i-phone 6 next year for less money (when the i-phone 7 will come out) ?
Because THAT is the anti-deflationary argument: people won't buy stuff TODAY because the SAME STUFF will be cheaper tomorrow. (not newer and better stuff, the SAME stuff). Well, we observe empirically that this is simply NOT TRUE.
Why did people buy personal computers when they knew that 3 years later, they could have gotten a machine with similar performance for a much lower price ?