Network code

Huh? 

I'm not sure what you're asking, but this is not the place to get any answer that's going to do you any good when you're outside of the service area. 🤦🏼‍♀️

If you're having a problem outside of the USA, you need to provide better information than you just did.  No information on what phone you're using, no information on what service plan or type of service plan you are on. No information on whether or not your phone is unlocked to use on a different service provider. No information on where in the world you are?

You probably mean the unlock code. To get an unlock code, you need to put in an unlock request:

https://att.com/deviceunlock