I can't disagree with Klauss.
Allowing C Band cellular except near airports is fine for normal airline operations, but what happens when an airplane has a distress condition and is off course? It may be flying close to cell sites, perhaps on a hilltop where they are often sited, and be deprived of height information at the very time when it is most vital.
And how does this help with low level operations over urban areas with a high density of cellular activity?
This really does seem another case of "We'll try it and see if it works". And we all know where that has led to recently.