This one is a shield: http://dx.com/p/manolins-sim-900-gsm-gprs-shield-expansion-board-wireless-module-w-antenna-for-arduino-black-215144 http://dx.com/p/manoli

This one is a shield: http://dx.com/p/manolins-sim-900-gsm-gprs-shield-expansion-board-wireless-module-w-antenna-for-arduino-black-215144 http://dx.com/p/manolins-sim-900-gsm-gprs-shield-expansion-b... And so is this: http://dx.com/p/arduino-compatible-gsm-gprs-shield-wireless-extension-board-module-w-antenna-adapter-144865 http://dx.com/p/arduino-compatible-gsm-gprs-shield-wireless-... And this (includes an Arduino Uno compatible board for $80):http://dx.com/p/elecfreaks-diy-gprs-gsm-learning-development-set-works-with-arduino-products-222149 http://dx.com/p/elecfreaks-diy-gprs-gsm-learning-development...