I'm about to embark on my first project using GSM. My requirements are quite simple: I just want the Arduino to receive SMS messages then act based on what was in the message. I won't need to send messages, make calls, or send/receive data over the phone network.
I'm in the UK and wondering about the sim card. If I order a free PAYG sim from Vodafone and never top up, will I be able to receive SMS messages at any point in the future without ever paying?