Truth be told I did eventually find it late last night and was going to update my post here.
I appreciate you reconfirming where this bugger is located.
It's a subtle thing and I wonder how many people even know this iOS feature exists. At least on Sprint is was fairly straight forward as a selectable free feature "Calls on iCloud Devices" if memory serves me correctly.
All the best,
It's really buried down in there. When first you log in, on the top right corner click on "My account," then "Profile". At the bottom of the next screen, you should see "Multiple Devices." Click that, and on the next screen make sure that DIGITS is enabled. Here's what mine looks like.
T-Mobile's mmWave network is impressive in that it's still the largest mmWave network in NYC despite them pretty much not working on it at all for over a year however, speeds on mmWave in my experience are always slower than midband. It's not like T-Mobile lacks the spectrum to provide Verizon-like mmWave speeds. They got 400MHz of 39GHz spectrum in Auction 103 back in December 2019. In spite of that they insist on using the 50MHz + 50MHz of 28GHz.
I don't know why they don't just overlay their macro footprint again with n260 antennas like they did before and provide those gigabit speeds across all of Manhattan and parts of the outer boroughs. They say that NYC is one of their markets where they have implemented their layer-cake strategy but their mmWave layer in it's current state is not as much of a capacity layer as they advertise given n41 has higher throughput both theoretically and on average than their mmWave network here.