SIM800L vs SIM900A GSM Modules
GSM modules use a SIM card and an RF chip to connect to the internet and phone network, providing microcontrollers with the capability to make calls and send SMS messages.
SIM900A GSM Module
The SIM900A is a readily available GSM/GPRS module,used in many mobile phones and PDA. The module can also be used for developing IOT (Internet of Things) and Embedded Applications.