How can I make a T-Mobile S4 work with Att's network?

[AC Question]

I have a TM s4. I want to use that s4 on Att. I was wondering, could I order an Att logic board, install it in the phone and use it with Att? Are there any hardware differences that would prevent this transfer from working as simply as I think it'd would?
Also, I want to learn to flash phones from one carrier to the next, but I can't find good sources to teach myself. I've rooted and unrooted phones before, but I don't know the general basics of flashing to different carriers. I'm a novice when it comes to this.
Flashing might be simpler than changing internals, but I do common phone repairs anyway. So, its no big deal. But it'd be really helpful if I got a better grasp on flashing phones. It would save people money and give me more business. Can anyone help? Thanks a lot for your time and information.

 

[spagman]

All you would have to do is Sim /Network unlock the phone and change APN settings.

Naturally you would need an AT&T sim card.

Do not flash at&t firmware on your T-Mobile S4 or you will hard brick it.

You would use at&t firmware on T-Mobile network.

That's it.