That is, they inspect your traffic and don't charge your bandwidth quota for network traffic with TMobile-selected music streaming services (Spotify, Google Play, etc).
They do DPI for other purposes though, such as ensuring that you don't tether without paying (if you use a desktop browser user agent, it'll count your tethering quota separately -- even if you spoof the UA from your phone's browser), and for "caching" HTTP traffic (you'll see a 'X-Via: Harmony proxy' header on any HTTP traffic, on any port).
They also hijack DNS NXDOMAIN for ad-filled pages, with no usable opt out ("opt out" uses a cookie that uses javascript to serve the page anyway, then hide it with a fake nginx 404)
Been meaning to try to dump some traffic so I can see more of what's going on.
I don't know about T-Mobile's ways of detection, but AT&T is detecting[0] tethering users by checking the network packets TTL values: If you are tethering then the TTL on their side will be below the expected value of mobile OS's default TTL. There are apps which can hide your tethering usage by altering your device's default TTL. You should still use a mobile browser's UA string, of course.
[0] - http://www.redmondpie.com/bypass-network-carriers-tether-det...
Apparently some IP packets are more equal than others.
I don't know. There are some lines I'm willing to cross and feel completely ethical, and bypassing stupid arbitrary net-neutrality rules is one of them.
I paid for the data. There is no difference if I use the data request comes from my mobile device or if it comes from my laptop connected to my mobile device.
Price discrimination is not a god given right nor is it criminal (usually) to avoid. (I can't think of a case where avoiding price discrimination is criminal, but I'm sure there is)
On one hand, it sounds reasonably "fair" for everyone involved. It seems that T-Mo is committed to impartiality (the site repeatedly mentions that all legal music services are eligible). They aren't double-dipping, since it's on top of the metered bandwidth you paid for (as opposed to charging the user for unlimited/unmetered data and then throttling services that don't pay up).
On the other hand, it's terribly opaque. Are they charging the streaming providers? Do the providers need to install dedicated proxies for T-Mo customers? Are they charging everyone the same? Is every service on the same terms? It's quite obvious that they have a cross-promotion deal with Rhapsody, but does Rhapsody get preferential treatment?
It seems that T-Mo are aiming for a compromise in regards to net neutrality. It doesn't seem too bad at this point, but there's always the risk of a slippery slope.
It's really just a marketing technique. Even though music streaming can use a significant amount of data, it's at a safely capped rate. It's probably a lot more effective to market "unlimited music streaming" to the general populace than "500mb more data".
It's in the same vein as, "unlimited in-network calls".
I just feel like folks don't realize the fact that net neutrality has never purely existed, not since peering agreements were first established.
It makes it harder for other businesses to enter the same market, as their offerings will not be zero-rated without an agreement with T-Mobile.
Any measure that makes it more difficult for companies to complete will ultimately harm consumers in the long run. So the only people this benefits, ultimately, are the incumbent providers, because it makes their market less competitive. Startups, for one, definitely lose: http://avc.com/2014/01/vc-pitches-in-a-year-or-two/
Data caps on cellular data plans already exist, so getting uncapped data for specific services does only benefit the consumer.
Your generic "net neutrality is good" arguments don't apply here, where net neutrality has been broken for years. Net neutrality hasn't ever existed on the web, let alone cellular data plans, anyway.
Honestly, their music thing doesn't bother me too much. They included nearly every major service. It doesn't seem like they're playing favorites.