> I would love to have a phone that has an active AT&T, T-Mobile, and Verizon SIM at the same time.
If you are not aware, US Mobile offers a Super Carrier package that one account can use all three. https://www.usmobile.com/networks
I don't use them, only read about it on r/nocontract.
That's interesting, but it doesn't allow you to use all three at the same time unless you have a phone that can have three active SIMs.
Stored SIMs/eSIMs is not the same as active SIMs/eSIMs.