Not sure, I use a corded phone.
The only way I guess is to try it, Cheap cordless phone and RJ11 to BT adaptor should be achievable for less than £20.
It may be a Three only thing as I believe that they use the 4G signal for voice as well as data.
We obviously need a telecommunications expert to give us chapter and verse.
I only found out because the original three router supplied with their original homefi plan said voice calls could not be made through the RJ11 socket, which made me think it had been disabled by Three and that if I purchased a non Three router and a cheap phone it may well work. It did!!!!