My experience with Home Assistant

A letter from Swisscom arrived two years ago and created a problem for the management of the heating of the house in the mountains. Because they informed us of the termination in end of 2020 of the GSM or 2G (old generation telephony) service. The current modem in the control module installed 7 years ago is not compatible with 3G or higher and therefore needed to be replaced. But with what?