I am trying to interface both GSM modem and bluetooth module to a same arduino UNO and both the devices uses different baud rates. help me out of this.
Use the hardware serial port for one device - Serial.begin(xxxxx), and SoftwareSerial(xxxxx) for the other?
What @dannable says is practical if you don't need to use HardwareSerial for communication with the PC. Also you will need to disconnect the device from it to upload a new program.
I would suggest using a Mega that has 3 spare Hardware Serial ports especially if you are a beginner.
...R
It is quite practical to use Uno, and makes quite lot of sense if you already have one. GSM shields typically have jumpers for them to use software serial, and you can properly upload and debug a programme with the bluetooth disconnected. Once done the bluetooth is connected and you are off and running. The vital thing to be aware of is that there is no difference in programming between serial monitor and bluetooth. Arduino doesn't care what it is talking to. So I don't think it is a case of one or the other, it is hardware serial for bluetooth and software serial for GSM.