Do T-Mobile and AT&T still have the roaming agreements with each other in place from back in the day when they were SBC/PacBell and Voicestream respectively ? I

Do T-Mobile and AT&T still have the roaming agreements with each other in place from back in the day when they were SBC/PacBell and Voicestream respectively ? I seem to remember in the early days of T-Mobile in California for the most part you were roaming on AT&T and T-Mobile branded phones had the firmware hacked to show 'T-Mobile' instead of 'SBC'. (I noticed a month or so ago my T-Mobile SIM ended up on an AT&T network when I was out in the wilds of Arizona so have been curious if this was still the case)