@dbread This is probably not the best way, but I can do it by sending an XMPP message to a number through jmp.chat, though you have to pay for it. If your device is offline then I guess this couldn't work, but then how would you send anything?
@dbread Maybe include a cellular modem with SMS support and a simple program to send them out. I remember using a GSM modem here years ago that was USB and had such a program included for sending and receiving SMS.