I still dont think the OP gets it.
The $99 price point you saw on the website is the subsidized price that the carrier has set. ALL 4 major carriers do this. That phone out right is a 500-650 phone. What T-Mobile is doing is allowing you to bring your own device and pay ONLY the air time usage fees. MetroPCS and Virgini (i think Virgin) you have to pay full price for the phone and get service cheap. Ill take my business line for example.
I signed up with TMO and brought my own equipment, $15 for air time (voice / MMS / SMS ) and $20 for data (unlimited) plus taxes. I pay around 50 bucks a month.
A few months after the HTC One came out. I thought ok i like it ill get one, what are my options. Option 1 is buy outright for 550. Option 2 is pay $99 down and then 20 payments of $20 added to my monthly bill. I went with option 2. So now my bill is closer to 70 a month. Which is still 10 bucks cheaper then what i was paying with Sprint before I left them.
Once the phone is paid off im back down to 50 bucks a month. I can also pay my phone off early if i want. SO if i get a great christmas bonus and pay it off early BAM im back down to 50 bucks a month for my montly air time bill. But wait, with Sprint my bill was always the same. I was with them 11 years and many of those years i was out of contract and using a used device i paid full price for. So for me the T-Mobile pricing model makes a whole lot of sense.
As far as you justifying not paying 3/4 rent thats a bad comparison, in my opinion. On your example you would have paid $27 a month for that awesome phone you wanted. Thats the rent to own price. With the $459 price thats the i paid for i own it price. Its a one time fee and your monthly air time would be cheaper.
With all the used iPhones and Android units out there its an awesome idea to buy a good used device then go to T-Mobile and pay just the air time usage. Its one of the main reasons i switched. That and the fact that Network Vision caused my Sprint device to get texts really late, missed a lot of calls and data speeds were worse. 4 months into Sprint LTE roll out in Dallas i couldnt get LTE where i worked or lived. But When T-Mobile switched on LTE i got it day one at home, at work, and many other places.. So yeah I went from being a Sprint fan boy to a T-Mobile fan boy and im proud to say the grass is way greener on this side of the fence.