An SMS gateway is used by cell phone networks as a means to route text messages through the system and store the information contained within the message before sending it to the intended recipient.
Different networks use different protocols, so the gateway acts as a means for the messages to pass through the unique gateway in order to reach the correct provider and, therefore, end user.
If you think of it as an actual gate, and say for example you are with Verizon. Lots of messages would queue at that gate, but only the ones with the passcode or key to the gate could get through, others would be diverted to AT&T, etc.
That's why, when you manually enter the SMS setup details of a new phone (actually this doesn't happen now but it did 10-15 years ago) there is a SMS gateway number that is entered and that is usually unique to the cell network that you are on. I say usually because, some cell networks allow smaller companies to set up and use their towers, etc. In this case they may share an SMS gateway code.
Different networks use different protocols, so the gateway acts as a means for the messages to pass through the unique gateway in order to reach the correct provider and, therefore, end user.
If you think of it as an actual gate, and say for example you are with Verizon. Lots of messages would queue at that gate, but only the ones with the passcode or key to the gate could get through, others would be diverted to AT&T, etc.
That's why, when you manually enter the SMS setup details of a new phone (actually this doesn't happen now but it did 10-15 years ago) there is a SMS gateway number that is entered and that is usually unique to the cell network that you are on. I say usually because, some cell networks allow smaller companies to set up and use their towers, etc. In this case they may share an SMS gateway code.