Innanzitutto grazie dell'aiuto. Lo schema mi diventa difficile postartelo perchè non ne ho uno nemmeno io per il programma invece te lo posto qui sotto:

#include
#include
#include
#include
#include
#include
#include

#pragma config OSC = INTIO7, WDT=OFF, MCLRE = OFF,DEBUG = OFF,LVP = OFF
#pragma config PBADEN = OFF
void arraytostring(void);
void getbyte(void);
void message(void);
char j=0;
char inbyte[50];
char x = 0;
char y = 0;

void getbyte(void)
{
char x = 0;
char y = 0;
if(RCSTAbits.OERR)
{
RCSTAbits.CREN=0;
Nop();
RCSTAbits.CREN=1;
}
while(x !=10 )
{
while (!DataRdyUSART());
if(RCSTAbits.OERR)
{
RCSTAbits.CREN=0;
Nop();
RCSTAbits.CREN=1;
}
x = getcUSART( );
if (x == 'O')
{
while (!DataRdyUSART());
x = getcUSART( );

if (x == 'K')
{
PORTAbits.RA0=1;
Delay10KTCYx(255);
PORTAbits.RA0=0;
Delay10KTCYx(200); // hai ricevuto il comando OK
}

}
}
}

void message(void)
{
char x,a,b,c,d,i = 0;
char y = 0;
for (i=0;i<20;i++)
{
if(RCSTAbits.OERR)
{
RCSTAbits.CREN=0;
Nop();
RCSTAbits.CREN=1;
}

while (!DataRdyUSART());
if(RCSTAbits.OERR)
{
RCSTAbits.CREN=0;
Nop();
RCSTAbits.CREN=1;
}
a = getcUSART( );
}
a = getcUSART( );
i=i+1;

}

void main(void)
{

OSCCON = 0b01110110;

ADCON1 = 0b00001111;

// Imposto PORTA tutti uscite
LATA = 0x00;
TRISA = 0x00;

// Imposto PORTB tutti uscite
LATB = 0x00;
TRISB = 0x00;
// Imposto PORTC tutti ingressi
LATC = 0x00;
TRISC = 0xFF;
// Imposto PORTD tutte uscite
LATD = 0x00;
TRISD = 0x00;
// Imposto PORTE tutti ingressi
LATE = 0x00;
TRISE = 0x07;

RCSTAbits.SPEN=1;
LATC=0;
TRISC=255;
TRISB=0b01000000;

PORTBbits.RB6=1;
Delay10KTCYx(255);
PORTBbits.RB6=0;
Delay10KTCYx(240);
PORTBbits.RB6=1;
PORTAbits.RA0=1;
Delay10KTCYx(255);
PORTAbits.RA0=0;
Delay10KTCYx(200);

// Quarzo 8MHz
// Formato 8 bit
// 1 bit di stop
// Baud rate 9600bit/s
// Interruzioni disattive
OpenUSART( USART_TX_INT_OFF &
USART_RX_INT_OFF &
USART_ASYNCH_MODE &
USART_EIGHT_BIT &
USART_CONT_RX &
USART_BRGH_HIGH,
51);
while (1)
{
const unsigned char corretto[3]={'O','K','\0'};
unsigned char i=0;
char inbyte[50];

Delay10KTCYx(40);
putrsUSART((const far rom char *)"AT\r\n");// AT command test
while(!BusyUSART());
getbyte();
Delay10KTCYx(200);
// arraytostring();

putrsUSART((const far rom char *)"AT+CPIN=1017\r\n");// AT command test
while(!BusyUSART());
Delay10KTCYx(200);
putrsUSART ((const far rom char *)"AT+CMGF=1\n\r"); // SMS format type; 1=text
while(!BusyUSART());
putrsUSART((const far rom char *)"AT+CMGR=4\r\n");
while(!BusyUSART());
message();

Delay10KTCYx(200);