> I am wondering how did they get their data especially for Switzerland. Here most of the plans have unlimited GB, so getting the price of a single one is quite tricky.
Not sure where you get that impression, but I don't think it is true at all. The following are the standard CH mobile plans by the largest providers in Switzerland.
Swisscom: 3×unlimited, 3×limited
Salt: 3×unlimited, 2×limited
Sunrise: 1×unlimited, 2×limited
In total they have 7 unlimited and 7 limited plans. The unlimited are mostly very expensive. Also note that the article mentioned they measured 14 plans in total which exactly matches the total number of plans above. But that of course might be a coincidence. Most plans of smaller providers are also limited in my experience.