A first device communicates with a remote second device by sending an SMS message that includes an encrypted first device phone number portion and a command, which may also be encrypted. The second device receives the SMS message and decrypts the encrypted first device phone number portion to verify the authenticity of the message by comparing it with a first device phone number included with the message by a cellular carrier. Successful decryption authenticates the first device, and the command is then executed, after being decrypted if it had been encrypted. Further authentication can optionally include decrypting an encrypted unique device identifier and/or phone number of the second device. The second device may also consider an embedded time stamp to determine whether the command is superseded by a subsequently issued command.