Arduino Nano and SIM900 - Is my schematics wrong ?

Hello guys,

That is the schematics

That is the very basic program I am trying

#include <SoftwareSerial.h>

SoftwareSerial mySerial(4, 5); // SoftwareSerial RX, TX

void setup() {
mySerial.begin(57600);
Serial.begin(57600);

}

void loop() {
if (mySerial.available()) {
int inByte = mySerial.read();
Serial.write(inByte);
}
if (Serial.available()) {
int inByte = Serial.read();
mySerial.write(inByte);
}
}

I am only getting special caracters when sending AT commands through Serial Monitor. I am not getting OK or readable letters; Example : if i type AT, I get �ªÃ�…ªÕdþ, and same whatever the baud speed

Any idea ?