Moving att prepaid BYOD SIM from an old Samsung Galaxy J7 to a new Galaxy A54 phone

This appears to be the correct article: 

https://www.att.com/support/article/wireless/KM1001034/

it says to:

AT&T Prepaid® SIM card

Follow these steps before you turn off your device.

1. Go to att.com/myprepaid.
2. Select My Device and then Update Device. Don't know your IMEI? Enter *#06# on your phone's keypad to get it.
3. Enter the SIM card number and then select Continue.

...

Data services don’t work after SIM swap

• Swapping a SIM card from a basic phone to a smartphone or tablet? We’ll add a compatible data plan when the device activates on our network. Or, you can call us to add it.
• Can’t use data after swapping the SIM, and confirming, or adding a data plan? You may have to program the correct access point name (APN) and multimedia messaging service (MMS) data settings.

Now that we have these instructions, all is not swell and rosy.  There's the bit about "Enter the SIM card number"  which you're supposed to do "before you turn off your device", however, you'd have to remove the SIM to see its number, right?  I'm not sure that this is even necessary or helpful.  Again, I'm not a AT&T PREPAID expert (and I did not sleep in a Holiday Inn Express last night), but these instructions at least are in the ballpark with what I'd expect.

Yes.

As long as the phone is compatible and the SIM card is the same size all you do is move the SIM card.

https://www.att.com/buy/byod/identify?devicetype=phone

Thanks formerlyknownas.  You also provided a link.  Just to clarify, that link goes through 5 steps for "Bring Your Own Device" (see pic below), including "2-Identify your device", "3-Choose activation type",  "4-Choose your plan", and "5-Review your cart."  Is that link ONLY if I did not already have an old ATT BYOD SIM card for the new phone?  Do I need to do anything on that site?  Just not sure what the purpose of that link is, if as you state, "all you do is move the SIM card".  Thanks.

@atthelp, I already have a prepaid sim card and account activated on my old byod phone.  I just want to move that sim card (and account and phone number) over to a new byod phone.  Do I still have to go through the process of activating the old sim again on the new byod phone and set up payments, etc. again?

@formerlyknownas  why do we let ATTHelp post here again?

@wingtong168  I am not an AT&T PREPAID expert, but my understanding is that if you already have an account, and an active SIM that physically fits in your new phone, the ONLY thing you need to do is move the SIM to the new phone.  Sure, you can check the IMEI for compatibility, but I'm 95% sure you do NOT want to follow those instructions otherwise.

thanks JefferMC.

@ATThelp: in your instructions, no. 9 states, "View your new phone number and restart your device."

- I do not want a "new" phone number, I want to keep my old existing phone number on the old sim card that was used on my old device, BUT ONLY want to move that old sim card from my old device to a new device and keep the old phone number.  Can you clarify?

Oh for goodness sakes.

The IMEI check is there just to make sure your phone is compatible. 

*If it offers to send you a SIM card, you don't need one , but that means you have a compatible device

@JefferMC 

Thanks for chiming in. I should have known better than to give vague instructions - I guess.

As for ATT no help at all, at least they're consistent at not reading the posts

Hello @wingtong168, thank you for contacting AT&T Community Forums. 

We'd really be happy to answer your question. Since your new phone 'Galaxy A54 5G' unlocked, you can use your old prepaid BYOD SIM to your new phone. 

If you have any other questions, please let us know! We're happy to assist you. 

Thank you for reaching out to our AT&T Community.

-Sia, AT&T Community Specialist.