arduino and gsm module receive
Most probably you are using sim900 or sim800 module. These modules would be either fixed to a certain baudrate like 9600 or 115200, OR the module might be at auto-baud mode.

In auto baud mode you need to send AT\r to the modem after the modem is switched ON so it can know what baud you are using.

Please check the following...


GSM Modem/Module not responding to AT commands after firmware Upgrade??
Serial port AN