What is "subsidy code"?

It would help if you gave your location.

If this iPhone you are about to buy was sold new as carrier locked with a designated provider and has been hacked to be unlocked, hacking an iPhone for any reason is against Apple's license agreement for the iPhone, is not supported by Apple directly or indirectly via these discussions, and voids the warranty.

The iPhone is built and programmed to be specific to your country's carrier. If Israel has a carrier and it supports the iPhone, then they would be the ones you purchase it from.

Each country has a different set of codes they enter to not only make it legit, but to avoid overseas charges as well.

If you are now living in the USA, congrats. If you are taking the iPhone back to Israel, note the message above.

The US iPhone is carrier locked to ATT and will not work with an Israeli SIM.

It is not true. If the seller is selling a US iPhone in Israel and has been hacked. If you upgrade or restore it, it will become relocked to ATT in the US.

Did I say something about hack?

No, I did, and you did also without using the word hack.

Copied from the first sentence in your original post.

*and is it true that once entered the locked phone becomes permanently unlocked just like a simfree officially unlocked iPhone?*

If this iPhone is not already officially unlocked, this means it was sold new as carrier locked, and the ONLY way to unlock an iPhone that was sold new as carrier locked is via a hack.

This is called reading what is provided and using common sense.