It seems it's still available, you just can't order it in person in a T-mobile store:
http://prepaid-phones.t-mobile.com/prepaid-plans
Is there something here I'm missing?
I can confirm that it is still available as I just activated it myself, and without going through Walmart or online activation as is stipulated on the page linked to above. It was, however, quite a pain to go through.
I switched to T-Mobile from Verizon just two months ago and after looking at my first bill I realized that I was hardly using voice and text messages (I have an iPhone with iMessage). I know that most of the savings discussed here advocate forgoing data, however, in my case I was willing to forgo voice/text and use data to compensate by using FaceTime Audio (free), iMessage (free), and Skype to place phone calls if I go over the allotted 100 minutes.
Anyway, I called in and explained that I wished to change from my post-paid plan to this pre-paid plan. I had to be transferred to the pre-paid department, which I can report, is not nearly as helpful or friendly as the post-paid department, who eventually changed me over. The hassle began when they didn't tell me that they were going to "flip the switch" yet and our call suddenly dropped. My phone reported no service so I did a soft reset and immediately got a text from T-mobile welcoming me to their pre-paid service. I tried calling 611 to figure out what happened to find that my balance was $0.01 and was consequently unable to make any calls. After calling from a friend's phone I got them to prorate $20 to my pre-paid balance as I still had about 15 days left in my billing cycle, paid the remaining $10, and was good to go.
For my purposes, this plan is incredible. I get unlimited data, of which 5GB is 4G LTE (really the only usable portion), 100 minutes of call time, which is sufficient for incoming calls from doctors, etc. (really the only people I can't call with FaceTime audio as most of my friends/family have iPhones), and unlimited domestic and international text messages, which I hardly use.
For those times that I do need to call I use either LINE or Skype. Line charges $0.02/min for calls within the US (and cheap international rates) and Skype is $0.023/min. Skype also offers unlimited calls for $2.99/mo but I'm holding off on that until I see whether I really need more than 100 or so extra minutes per month.
Overall, I'm very pleased with the plan and almost can't believe that I'm able to get so much data for only $30/mo. For reference, I was paying $60/mo (plus taxes and fees) for only 3GB high-speed data. The only difference was unlimited calling, which I've decided isn't necessary for me. This means $30/mo or $360/yr savings (actually, it's a bit more considering the taxes and fees are more on the post-paid plans).