The code uses the SMSTO format that both iPhone and Android read from the camera. The number is stored in international format; write it as you like and we tidy it.
A pre-filled word like "BOOK" or "MENU" lets you sort replies without any software. Keep it short so the code stays small.
Questions
Does it send the message automatically?
No. The person sees the message and taps send. Nothing goes out without them.