Arduino - SIM900

Hello.
I want to make a project using an arduino and SIM900 to send a sms,but doesn’t work and I want your help to figure it out,because I do not understand some things.
Code:

#include <SoftwareSerial.h>

SoftwareSerial mySerial(8, 7); 

void setup()
{
  Serial.begin(9600);
  mySerial.begin(9600);

  Serial.println("Initializing..."); 
  delay(1000);
  mySerial.println("AT+CPIN = \"7394\""); // sim password
  updateSerial();
  
  mySerial.println("AT"); 
  updateSerial();

  mySerial.println("AT+CMGF=1");
  updateSerial();

  mySerial.println("AT+CMGS=\"+30XXXXXXXXXX\"");  // I don't show phone number 
  updateSerial();
  mySerial.print("Hello world"); //text content
  updateSerial();
  mySerial.write(26);
}

void loop()
{
}

void updateSerial()
{
  delay(500);
  while (Serial.available()) 
  {
    mySerial.write(Serial.read());//Forward what Serial received to Software Serial Port
  }
  while(mySerial.available()) 
  {
    Serial.write(mySerial.read());//Forward what Software Serial received to Serial Port
  }
}

Output:

Initializing…
AT+CPIN = "7394"

OK
AT

OK
AT+CMGF=1

OK

+CREG: 2
AT+CMGS="+30XXXXXXXXXX" // I don’t show phone number right here

> Hello world

So,I don’t receive any messages.
Also,I don’t understand what is the meaning of +CREG: 2

I searched in google and I found:
2 not registered, but MT is currently searching a new operator to register to
but I don’t understand what is the meaning of this.

I use Arduino Uno and here is SIM900

Thanks.

but I don't understand what is the meaning of this.

exactly what it says. Your unit has not registered with a network, but is searching. Has your simcard been activated ? have you tried AT+COPS=?to get a network list ?

SIM900 is a 2G device. The first thing you need to do is ensure that your provider has a 2G service. There is a good chance that it doesn't.