And offline playlists. Apart from the US there aren't many countries that offer unlimited mobile data plans for a reasonable price. So for me, offline playing is a very big deal, since that's how I listen to most of my music when I'm away from home.
I have the 3 unlimited plan but also Spotify premium because it's just easier having offline synced playlists, especially for train journeys when signal is always spotty.
To be fair, T-Mobile doesn't advertise their plans as "unlimited", they advertise them as 500mb/2.5gb/5gb at 4G speed. It's only $10/month more to bump up to 2.5GB.
And if you paid the extra $20 a month, you would have the Unlimited LTE plan instead of the Unlimited 2G plan with 500mB of LTE. $70 is still reasonable in my eyes.