The free item I would like to recommend today is SIM808 GPRS/GSM+GPS+Bluetooth Shield . This is one of hottest products on our site. Except for popular ESP8266, SIM808 can be also used in IoT projects. One of Elecrow engineer did a remote control project based on SIM900, the old version of SIM808. The Remote Control Via GPRS/GSM tutorial is completely recorded on Elecrow instructables channel.
We're excited to see what you will create with SIM808. (Send the link of your project to email@example.com to get a refund)