I am using P89V51Rd2 microcontroler for my security system project It is requred me to recive and decode sms by using GSM modembut,the serial interrupt had been used for another application Is there any gsm modem that provides status at it pins when it recive sms or call.
To be able to read out the SMS, you do need a serial port. While it is possible to have a multiplexer, so the microcontroller switches between different external devices (only works if microcontroller is master, and they are silent while muxed away), that is not a good design.
Select a processor with two UART. You really, really want to have multiple UART if you have several devices connected that makes use of asynchronous serial communication.
As Per says, just get a microcontroller with sufficient serial ports!