The Shield GPRS/GSM SIM900 is the easiest way to connect the Arduino to the network, allowing you to send and receive text messages (SMS), make voice calls, and even connect to the Internet via GPRS, thus entering the world of the Internet of Things (IoT). The Shield SIM900 operates on GSM 850/900/1800/1900 MHz bands. All you need to add mobile phone functionality to your project is a SIM card (Entel, Movistar, or Claro), and now you can start sending messages, making calls, among other things.