Expensive in time compared to benefit accrued/harm done. At a minimum you have to spend a person's time on it, both in the gathering of a bunch of used phones,

Expensive in time compared to benefit accrued/harm done. At a minimum you have to spend a person's time on it, both in the gathering of a bunch of used phones, the setting up of many phone lines, and the actual work of walking on the street. A small street seeming busy on Google Maps doesn't really matter that much. Especially, if the street is not actually busy, since that's kind of an indicator that people don't really want to use it anyway. So the amount of traffic you'd potentially divert is similarly small. This seems really obvious to me, so if it doesn't seem that way to you, maybe we just have different priors. I can't explain it any better than this, though.