Aerostar,
okay it arrived yesterday and it worked a treat. Almost a direct drop-in replacement for my older 3G module (starts message indexing at 1 instead of 0).

https://www.aliexpress.com/item/1005002280354604.html

I purchased the A7670E module which appeared to be the last one of but I probably could've used the A7670C just as effectively. There are cheaper modules, but this one is very versatile and allows 5V interfacing.

So, only 4 wires required: pos & neg rails and the receive + transmit serial wires. Uses AT commands: https://www.ktron.in/wp-content/uplo...al_V1.06-4.pdf

The module needs to be turned on (there's a microswitch button) which you can pull to ground via your PIC micro to avoid needing to manually press upon power up.

My application is for my wife and I to gather the up or down status of our garage door ie. we leave the house and are unsure whether we remember to lower the door. This allows us to send a text message to the module and receive the status and to also lower the door via SMS if needed.

Troy