“The Rebbi told him that it was like putting a piece of matzah into a dish full of Chometz – not only does the Chometz not become Kosher LePesach, but it actually makes the Matzah chometz too.”
This is nice and all but at the end of the day it is only your rabbis opinion. I need a smart device for work, so yes I would need either a smart phone or tablet anyway. But to say that smart phones are not suitable for most people, especially younger people, and therefore no one should have one, is not pashut in my opinion. Especially if it has a filter.