It is a good example you give with the mobile phone (and I agree in part). However, couldn't someone who was loud and discourteous who was pulled aside for the rule-breaking have a cause for pointing at you and saying why wasn't he breaking the rule? Which could lead to a slightly more nuanced contrast, when have you stepped over the guideline? Where that line is, will depend on the person who is going to say something.

I park my car outside my garage, which is technically illegal, but none of my neighbours have a problem with it, as everyone does it (or the verges). However, last Christmas, someone did have a problem with it, and the entire neighbourhood got fined after they called police! So, in this case, the rule is enforced by the squeakiest wheel!

... also, about the speed limits. I live on a small road with a limit of 30kph, for good reason, there are limited sight lines and lots of kids and schools. However, there are many people who treat it as a "guide" and choose to race through at speeds that are much much faster! In this case, I would wish that the limit was more strictly enforced, as it is too late to be enforced after an accident...

...but it is good that you point out the difference between rule and law. I hadn't thought about that when I posted the question, I was just using the two words as synonyms.