People like me eventually get fed up with artificially imposed data caps and will go elsewhere and not come back.
So, you will leave T-Mobile and not go back as well?
And once you realize after a certain amount of data used you will drop to 2g "unlimited" speeds and you get hardly no data off the network you will be leaving a carrier yet again.
Considering at least 20% of the US can't even get a T-Mobile signal AT ALL this is why Verizon can continue to get business and charge premium. Because they have a premium network. Good luck using your "unlimited 4G" when you leave the big city.
The SIM are where the account info is. Since unlimited data isn't offered and not in the system when the new SIM is program it's programed with the 2 GB data plan instead of unlimited. Supposedly there is some way to fix that but you have to tell them beforehand. I suspect the OP never specified that he had unlimited data which would have alerted teh CS rep to do the proper change to teh SIM card. So when the OP asked "Will this change my plan" the CS rep was correct as it does not if you're not on unlimited data. And since so few still have unlimited data and it has not been offered in nearly 4 years most reps would not think to ask.
You didn't need a SIM to make a phone work with WiFi. On the language screen when you first set up after a factory wipe
1 touch top left area below last language listed
2 touch top right area below last language listed
3 touch left bottom of screen corner
4 touch right bottom of screen corner
5 press and hold volume up
Now bypassed and WiFi ready.
Just to let you know I got my unlimited data back. It only took 5 reps and 1 manager. One of the reps confessed that the original reps stated that SHE used my upgrade which was a lie. I purchased my phone off of EBAY. She lied and they were in breach of contract.
If you have unlimited data plan, your contract for tha plan was over years ago. You are now on a month to month contract, which Verizon can end when they like, just as you can.
Think rental of an apartment. You sign a 2 year lease. At the end of the 2 year lease, you and the landlord continue on a month to month rental. That is what you have now....month to month.
Verizon didn't have to give the data plan back. There was no breach of contract.