char csq_query_msg[]="AT+CSQ\r";
char sms_hdr[]="AT+CMGS="0698090262"\r";
char csq_answer[5]={'0', '0', '0', '0', '0'};
char input_buffer[99];
char lettre = 'A';
char egal = '=';
char ctrlz = 26;
while(1){

    /* On attend un peu */
    compteur = 0;
    while(compteur<4000);

    /* On vide le buffer d'entrée */
    for(i=0; i<100; i++){
        input_buffer[i] = 0;
    }
    t = 0;

    /* On demande le CSQ */
    while(PIR1bits.TX1IF);
    puts1USART(csq_query_msg);

    /* On attend que le MODEM nous donne le CSQ (buffer input rempli) */
    while(t<20);

    /* On releve le CSQ */
    for(i=0; i<=5; i++){
        csq_answer[i] = input_buffer[i+18];
    }

    /* On envoi le sms */
    /* On envoi les headers */
    while(PIR1bits.TX1IF);
    puts1USART(sms_hdr);
    /* On envoi la lettre identifiant le sms */
    while(PIR1bits.TX1IF);
    if(lettre > 90)
     lettre = 65;
    Write1USART(lettre++);
    /* On envoi le egal */
    while(PIR1bits.TX1IF);
    Write1USART(egal);
    /* On envoi le relevé CSQ */
    for(i=0; i<=5; i++){
        while(PIR1bits.TX1IF);
        Write1USART(csq_answer[i]);
    }
    /* On envoi le CTRLZ */
    while(PIR1bits.TX1IF);
    Write1USART(ctrlz);

}

a mettre dans l'interrupt :

if(PIR1bits.RC1IF){
    input_buffer[t++] = RCREG1;
    if(t=99)
        t=0;
}