How to change baud rate mode of GSM900

Hi friends......actually im using arduino mega with sim900 module and by misktake i used the command AT+IPR=4800 and the baud rate changed to 4800 and now i need to change the mode to auto bauding once again but now im using the command AT+IPR=0 (0= autobauding) but it seems that the mode is not changed and when i send any command to the module i just receive junk it seems that bauding between SIM900 and arduino is not same. How to change the mode to autobauding once again please someone reply.


What does AT+IPR? return?

It gives `~ junk what should i do to resolve this problem?