visit the following link:

http://www.coineltech.com/gsm-sim900a-ttl

I have purchased this GSM modem from them they have sent me a product with four or five components missing on the board, the main reason why I chose this modem was the reason that it is having a metallic sim holder, they have provided me one with a plastic sim holder. Via email they told they are sending the parts and sim holder by courier on 23rd Jan 2015. They have not sent the same and are now keeping silent. One more cheater from Bangalore, there are several others like this so please beware and refrain from buying their products and services.