I have yet to encounter a kindergartner with a cell phone, but I have seen cellphones/smartphones carried by kids in upper elementary grades.
For you kindergarten parents—why not start to think about how you'll respond when your child asks to have his or her own smartphone?
My wife and I had it much easier when our children were growing up. Cellphones had not yet come into widespread use. Back then, the hot new technologies were pagers and portable music players—not iPods—but CD Walkmans.
When our middle-school aged kids began to say (with ample evidence) that "everyone has them" we relented and soon they were listening to their music through headphones pretty much all the time.
Talking to our kids got much harder. Even simple exchanges seemed more like interruptions greeted with rolled eyes and the removal of the headphones, and a sigh. Technology put a lot of distance between us and our own children. We have long felt that we made a mistake in caving to the "everyone has them" argument.
I know I'm not alone in feeling that way. I recently ran across this Youtube clip from the Conan O'Brien show with Louis C.K. talking about this very thing. If you haven't already seen it, have a look.