Barry, while I agree with you somewhat, I really don’t like the comparison between posessing a smartphone and walking out on the street.
When you walk out on the street, do you sometimes have an intense desire to look at pictures and videos that can destroy your neshama? Sure, there are billboards sometimes, and also scantily clad women. But the damage that you cause to your neshama by looking at these things is nowhere near the amount of damage that can be caused by using the dark side of the Internet.
The spiritual danger that is inherent in posessing a smartphone is many times worse than the danger in walking down the street, so the two can not be compared fairly.
Also, yes- smartphones are computers. But anyone with a life does not have 24/7 access to a computer, whereas your smartphone is always with you. By buying a smartphone, you are pretty much signing a contract with your Yetzer hara, allowing him to live with you 24/7, and promising that you will have what I think (little me 🙂 is the most powerful weapon he possesses.