iPhone Cellular Icon Meaning?
Does anyone know what the U and M symbols mean on the cellular connection icons?
iPhone 15 Pro Max
Question marked as
That's the initial of the label you gave each of the plans.
Only you can know what you named them, so only you can know what the U and M stand for.
Go to Settings ➜ Cellular and see what you labeled each plan there.
Using Dual SIM with an eSIM - Apple Support