SIM300 is a GSM/GPRS Modem with RS232. If you get "OK" status for commands like: "AT+CMGF=1" but errors like: '+CMS ERROR: SM BL not ready' for commands like: AT+CMGL="ALL", it just means that the SIM card is not inserted properly, though to the visible eyes it looks properly inserted. Just dis..
Featuring an industry-standard interface, the SIM900A delivers GSM/GPRS 900/1800MHz performance for voice, SMS, Data, and Fax in a small form factor and with low power consumption. With Board size of 75x54mm, and interfacing ports of Serial UART DB9 Female, TTL, Mic, Speaker, I2C, ADC, PWM (Floating..