In the IoT world the connectivity is a necessity but sometimes internet is not available, is expensive and we don't need a 24/7 connection. If a GSM signal is present we can use an old mobile to send and receive SMS.
A Nokia3310 with an home-made-regenerated battery is connect through the serial port at the Zero Pi. The communication uses the library gnokii and with an easy setup we can send and receive text messages from raspberry.