sending sms using pic16f877a and sim 300

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SMS

PIC

Hi I have a problem in sending message in project, I am using pic16f877a and sim300. the main function runs repeatedly. Some characters are missed in the sent sms. my program is like this...

void main()//main function
{
Serial_init();  // initialization of serial communication
Send_SMS();
}

void Serial_init()
{
TRISC=0XC0;
TXSTA=0x24;
SPBRG=129; // set baud rate 9600 Hz for 20MHz fosc
RCSTA=0x90;
TXIF=1;
}

void Send_SMS(void)
{
USART_puts("AT\0");
putch1(0x0D);
Delay_ms4M(200);
USART_puts("AT+CMGF=1\0");       // switch into text mode

putch1(0x0D);// ascii of Carriage Return
Delay_ms4M(200);
USART_puts("AT+CMGS=\"9741153218\"\0");   // send sms to the number
putch1(0x0D);
Delay_ms4M(200);
USART_puts("Hi this is working LOL\0"); // SMS text
putch1(0x0A); // new line
Delay_ms4M(200);
putch1(0x0D);
Delay_ms4M(100);
putch1(0x1A);   // ascii of 'substitute' i.e end of file
    }


    void USART_puts(const unsigned char *string)
    {

    while(*string)

putch1(*string++);

   }

   void putch1(unsigned char data)
   {
while(TXIF==0);
TXREG=data;
   }

Please help

additional details: all other programs run properly, but if I call send_sms function, "main" runs repeatedly and several messages are sent with missed characters.