SIM808 (ATE0) echo problem

unsigned char *at_cmd = "AT";
unsigned char *echo_off = "ATE0";
unsigned char *act_pro = "AT&W";
unsigned char *imei_cmd = "AT+GSN"; (and initialized some other AT commands in same format)
gsm_cmd(at_cmd);
__delay_ms(1000);
gsm_cmd(echo_off);
__delay_ms(1000);
gsm_cmd(act_pro);
__delay_ms(1000);
gsm_cmd(imei_cmd);
__delay_ms(1000);
unsigned char *sms_format = "AT+CMGF=1";void gsm_cmd(unsigned char *string)
/*{
    i=0;j=0;
    while(string!='\0')
    {
        if(string==0x5C) // Not to send '\' character
            i++;
        tx_data(string); // Send by serial communication
        i++;
    }
    tx_data(enter); // Send ASCII code for 'Enter' key(enter=0x0A) */

#include "p18f4580.h"
#include "xc.h"
#include "htc.h"
#include "stdio.h"
#include "string.h"
#include "stdlib.h"
// #include <delays.h>
#define FREQ 12000000
#define baud 9600
#define spbrg_value (((FREQ/64)/baud)-1)
 
unsigned char ctrl_z=0x1A; // terminate msg
unsigned char enter=0x0D; // carriage return
unsigned char l_feed=0x0A; // line feed
volatile unsigned char *data;

// PIC18F4580 Configuration Bit Settings

// 'C' source line config statements

#include <xc.h>

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.

// CONFIG1H
#pragma config OSC = XT         // Oscillator Selection bits (XT oscillator)
#pragma config FCMEN = OFF      // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor disabled)
#pragma config IESO = OFF       // Internal/External Oscillator Switchover bit (Oscillator Switchover mode disabled)

// CONFIG2L
#pragma config PWRT = OFF       // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = BOHW     // Brown-out Reset Enable bits (Brown-out Reset enabled in hardware only (SBOREN is disabled))
#pragma config BORV = 3         // Brown-out Reset Voltage bits (VBOR set to 2.1V)

// CONFIG2H
#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT disabled (control is placed on the SWDTEN bit))
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

// CONFIG3H
#pragma config PBADEN = ON      // PORTB A/D Enable bit (PORTB<4:0> pins are configured as analog input channels on Reset)
#pragma config LPT1OSC = OFF    // Low-Power Timer 1 Oscillator Enable bit (Timer1 configured for higher power operation)
#pragma config MCLRE = ON       // MCLR Pin Enable bit (MCLR pin enabled; RE3 input pin disabled)

// CONFIG4L
#pragma config STVREN = ON      // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)
#pragma config LVP = OFF        // Single-Supply ICSP Enable bit (Single-Supply ICSP disabled)
#pragma config BBSIZ = 1024     // Boot Block Size Select bit (1K words (2K bytes) boot block)
#pragma config XINST = OFF      // Extended Instruction Set Enable bit (Instruction set extension and Indexed Addressing mode disabled (Legacy mode))

// CONFIG5L
#pragma config CP0 = OFF        // Code Protection bit (Block 0 (000800-001FFFh) not code-protected)
#pragma config CP1 = OFF        // Code Protection bit (Block 1 (002000-003FFFh) not code-protected)
#pragma config CP2 = OFF        // Code Protection bit (Block 2 (004000-005FFFh) not code-protected)
#pragma config CP3 = OFF        // Code Protection bit (Block 3 (006000-007FFFh) not code-protected)

// CONFIG5H
#pragma config CPB = OFF        // Boot Block Code Protection bit (Boot block (000000-0007FFh) not code-protected)
#pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM not code-protected)

// CONFIG6L
#pragma config WRT0 = OFF       // Write Protection bit (Block 0 (000800-001FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (002000-003FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection bit (Block 2 (004000-005FFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection bit (Block 3 (006000-007FFFh) not write-protected)

// CONFIG6H
#pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) not write-protected)
#pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot block (000000-0007FFh) not write-protected)
#pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM not write-protected)

// CONFIG7L
#pragma config EBTR0 = OFF      // Table Read Protection bit (Block 0 (000800-001FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (002000-003FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection bit (Block 2 (004000-005FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection bit (Block 3 (006000-007FFFh) not protected from table reads executed in other blocks)

// CONFIG7H
#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot block (000000-0007FFh) not protected from table reads executed in other blocks)

The interrupt function SerialRxPinInterrupt() is automatically activated when there is any incoming at Rxd pin. The RCREG contents are stored in the string data[]. It is used in writing to LCD.
void gsm_cmd(unsigned char *string)
{
    i=0;j=0;
    while(string!='\0')
    {
        if(string==0x5C) // Not to send '\' character
            i++;
        tx_data(string); // Send by serial communication
        i++;
    }
    tx_data(enter);
}
For transmitting info from PIC to SIM808 ,I am using the function
void tx_data(unsigned char serial_data) // Transmit data function
{    
    while(PIR1bits.TXIF==0);
    TXREG=serial_data;
}
I am using interrupt function for receiving info from SIM
void interrupt SerialRxPinInterrupt() //Receive response of SIM808
{
data[j]= RCREG;  // Store the data into array when Reception interrupt occurs
value = RCREG;
j++;
}//declared data as volatile unsigned char