Send daily SMS messages using SeeedStudio GSM SIM900 and Arduino
See "Using GSM SIM900 Arduino.pdf" for full details
UPDATE FOR TIME LIBRARY
The Time Library changed for newer Arduino IDE, so you may need to download and install the custom Time Library for Arduino from:
https://github.com/PaulStoffregen/Time
You can download as Zip and then import into your Arduino IDE using Sketch -> Include Library -> Add ZIP File