// Connect to WIFI
AT+CWJAP="MYNET","MYPASSWORD"rn

/*
 *  Loop
 *
 *  Open TCP connection
 *  Send 10 bytes
 *  Close TCP Connection
 */
AT+CIPSTART="TCP","104.111.111.111",667rn
AT+CIPSEND=10rn1111122222rn
AT+CIPCLOSErn

Ncat: Connection from 111.111.111.111:11672.
1111122222
Ncat: Connection from 111.111.111.111:35756.
2AT+CIPCLO1111122222
Ncat: Connection from 111.111.111.111:8784.
1111122222
Ncat: Connection from 111.111.111.111:63288.
1111122222
Ncat: Connection from 111.111.111.111:28498.
1111122222
Ncat: Connection from 111.111.111.111:33319.
1111122222
Ncat: Connection from 111.111.111.111:35146.
1111122222
Ncat: Connection from 111.111.111.111:34454.
1111122222
Ncat: Connection from 111.111.111.111:33916.
1111122222
Ncat: Connection from 111.111.111.111:37095.
1111122222
Ncat: Connection from 111.111.111.111:12652.
1111122222
Ncat: Connection from 111.111.111.111:61951.
1111122222
Ncat: Connection from 111.111.111.111:27051.
1111122222
Ncat: Connection from 111.111.111.111:61870.
111122222A1111122222
Ncat: Connection from 111.111.111.111:38063.
1111122222
Ncat: Connection from 111.111.111.111:32270.

111122222A1111122222
2AT+CIPCLO1111122222

1. The data I receive from ESP8266 is for the most part 0x00, so I can't read and process the responses.
2. Not totally sure if this is correct: UBRR0 = ((( F_CPU / (BAUD * 16UL ))) - 1);
   In the original example, it had 'BAUD * 8', but it didn't work for me, when changing it to 16, esp8266 started to understand commands.

#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <util/delay.h>
#include <avr/interrupt.h>

#define F_CPU 8000000UL
#define BAUD  9600

char buffer[ 70 ];
int  received = 0;

void delayms( uint16_t millis )
{
    while ( millis )
    {
        _delay_ms( 1 );
        millis--;
    }
}

void blink_red()
{
     PORTB = 0b00000010;
    _delay_ms(10);
     PORTB = 0b00000000;
    _delay_ms(10);
}


void command_send( char *buf, int len )
{
    int i = 0;

    for( i=0; i<len; i++ )
    {
        blink_red();
        UDR0 = buf[i];
    }
}

int main( void )
{
    // Init serial
    DDRD    = 0b01101000;
    DDRB    = 0xFF;
    UBRR0   = ((( F_CPU / (BAUD * 16UL ))) - 1);
    UCSR0B  = _BV( RXEN0 ) | _BV( TXEN0 );
    UCSR0C  = 0b00000110;
    UCSR0B |= ( 1 << RXCIE0 );

    sei();

    command_send( "AT+CWJAP="XXXXXXX","XXXXXXXXXX"rn", 32 );
    _delay_ms( 15000 );

    while( 1 )
    {
        command_send( "AT+CIPSTART="TCP","111.111.111.111",667rn", 41 );
        char data[] = { "AT+CIPSEND=10rn1111122222" };
        _delay_ms( 30 * 1000 );
        command_send( data , 25 );
        _delay_ms( 30 * 1000 );
        command_send( "AT+CIPCLOSErn", 13 );
        _delay_ms( 30 * 1000 );
    }

    return 0;
}

ISR( USART_RX_vect )
{
   char ReceivedByte;

   ReceivedByte       = UDR0;
   buffer[ received ] = ReceivedByte;

   received++;
}

CC=/usr/bin/avr-gcc
MEGA=328p
CFLAGS=-g -Os -Wall -mcall-prologues -mmcu=atmega$(MEGA)
OBJ2HEX=/usr/bin/avr-objcopy
PROG=/usr/bin/avrdude
TARGET=esp8266
DEVICE=/dev/ttyACM0

program : $(TARGET).hex
        $(PROG) -c avrispv2 -p m$(MEGA) -P $(DEVICE) -e -B 2.0 -U lfuse:w:0xe2:m -U hfuse:w:0xd9:m
        $(PROG) -c avrispv2 -p m$(MEGA) -P $(DEVICE) -U flash:w:$(TARGET).hex

%.obj : %.o
        $(CC) $(CFLAGS) $< -o $@

%.hex : %.obj
        $(OBJ2HEX) -R .eeprom -O ihex $< $@

clean :
        rm -f *.hex *.obj *.o