#define USART_BAUDRATE 9600
#define BAUD_PRESCALE ((F_CPU/(USART_BAUDRATE * 16UL)) - 1)

int main (void)
{
cli();

lcd_init(LCD_DISP_ON);
lcd_puts("!LCD Test");
_delay_ms(1000);
lcd_clrscr();

UCSRB |= (1 << RXEN) | (1 << TXEN); // Turn on the transmission and reception circuitry
UCSRC |= (1 << URSEL) | (1 << UCSZ0) | (1 << UCSZ1); // Use 8-bit character sizes

UBRRL = BAUD_PRESCALE; // Load lower 8-bits of the baud rate value into the low byte of the UBRR register
UBRRH = (BAUD_PRESCALE >> 8); // Load upper 8-bits of the baud rate value into the high byte of the UBRR register

UCSRB = ((1<<TXEN)|(1<<RXEN) | (1<<RXCIE)); // Enable receiver and transmitter and receive complete interrupt
sei(); // Enable the Global Interrupt Enable flag so that interrupts can be processed

USART_Transmit("AT\r\n");

lcd_puts("!z"); //debug message
_delay_ms(1000);

USART_Transmit("AT+CSMINS?\r\n");
lcd_puts("!z"); //debug message

for (;;) {}
}

ISR(USART_RXC_vect)
{
char ReceivedByte;
ReceivedByte = UDR; // Fetch the recieved byte value into the variable "ByteReceived"

lcd_putc(ReceivedByte);

/*if(ReceivedByte=='O'||ReceivedByte=='o')
lcd_puts("(o)");
if(ReceivedByte=='K'||ReceivedByte=='k')
lcd_puts("(k)"); - и это писал, т.к. даже в кодировке LCD засомневался*/
}