OpenMQTTGateway/docs/setitup/gsm.md

GSM 2G gateway

Compatible parts

Module	Purpose
A6	GSM GPRS module
A7	GSM GPRS module with GPS

Hardware setup

Module Pin	NodeMCU / ESP8266 Pin
H_RXD	D6
H_TXD	D7
GND	GND
VCC5	MOSFET driven by D5

For VCC5 you can power it directly all the time with an USB cable or use a MOSFET like here

Don't use the nodemcu/wemos 5V pin for the A6/7 power, use a dedicated power supply for both or dedicated to the A6/7 with at least 2 amps ability.

So as to start your A6/7 module press the red button for 4 seconds, or link the PWR_KEY GPIO to VCC5.0 for the same time.