I've never been able to get a definitive answer and would appreciate it if someone is able to point to something tangible.
In the early days of mobile phone licensing (the Cellphone company buys a licence to operate the system) there was a prohibition of use in aeroplanes i.e. it was a condition of the operator's licence. Whether that is indeed true of later 3G and 4G licences I don't know, but that is the place to look.