Hi karthick,
*First we are writting data to fetch the address or commands to the slave i.e first we have to send the address which we have to read and then we will read the data.Two address you have to fetch in I2C one is Slave address and another one is Register address for reading the register data.
*As far as i go through the datasheet i can't find any way to configure both master and slave mode. you can achieve it by the program logic which will change the register values accordingly.
http://www.engineersgarage.com/articles/gsm-gprs-modules
http://www.engineersgarage.com/tutorials/gps-receivers-nmea-standards
http://www.engineersgarage.com/embedded/avr-microcontroller-projects/gps-interface-circuit