T-Mobile's IPv6 service is an IPv6-only service that uses NAT64 and DNS64 in the network to connect IPv6 mobile users with IPv4 content. We believe that the majority of the bandwidth consumed by IPv6 subscribers will be native end-to-end IPv6 without any translation required by the end of 2012 as major content providers like Google, Yahoo, Facebook, Microsoft, and many others have demonstrated during World IPv6 Day
They only mention the two Samsung Android models, but I'm pretty sure that the N900 will work with this as well. I'll have to give it a try, maybe this weekend.
That is correct, the N900 will work correctly. As will any Nokia Symbian S60 phone like the e73 and so on. They only listed the Samsungs since they are current. With Google now offering the Galaxy Nexus for $399, it is a pretty darn good deal.
4. My phone is not listed above, will it work with IPv6?
No, most phones do not have the Android radio firmware (RIL) that allows the phone to support IPv6 on the mobile interface. T-Mobile USA is encouraging all handset phone manufacturers to support IPv6. If more phones become available, we will update this site.
From what I understand, a lot of cell radios have the IP stack baked into the hardware/firmware, which means that getting IPv6 support is not as easy as upgrading the kernel. I don't know where this decision came from, but I imagine there is some reason for it.
It's mostly because of legacy. Your smartphone has (atleast) 2 operating system, there's the visible one (Android/iOS), and the one running the base band. The protocols used to talk to the cellular network is quite big, much, much bigger than just a TCP/IP stack, and there's usually more than one (often 2 or 3 of GSM, UMTS, LTE, CDMA). That part of the cellphone has evolved over the years, and when cellphones were able to connect to the internet over the cellular network, many stuck a TCP/IP stack in there as well, together with all the other protocols running on the baseband processor, and that decision has stuck. All this is abstracted away in android in the RIL, and while many(most?) Android devices does use the linux IP stack (as this picture conveys; http://www.kandroid.org/online-pdk/guide/telephony.html), not all do, and not all phones run Android - and are still leveraging the IP stack in the baseband. Cause it works, and it cost money to do something about it.
T-Mobile's IPv6 service is an IPv6-only service that uses NAT64 and DNS64 in the network to connect IPv6 mobile users with IPv4 content. We believe that the majority of the bandwidth consumed by IPv6 subscribers will be native end-to-end IPv6 without any translation required by the end of 2012 as major content providers like Google, Yahoo, Facebook, Microsoft, and many others have demonstrated during World IPv6 Day