You can find a list of phones to buy on their website (click "Mobile Service" at the very top right, then "Want a Phone"). You can also bring any T-Mobile phone (including 4G) and it will work without even unlocking.
Here is my break-down:
1) Truly unlimited minutes/text.
2) Data is unlimited, but speed-throttled at 4GB
(Most T-Mobile customers are 2GB, some are 5GB)
3) You can tether without seeing T-Mobiles upsell.do page.
4) If you don't like it within 14 days, you get your entire $49 back.
5) You can port your number as easily as any other carrier.
6) For the money saved, it was worth paying T-Mobile a $200 ETF
7) If you get 3 other people to sign up, they pay you $20/mo, every month for as long as they have service. Keep signing people up, keep making money more money, no limit, extra bonuses.
Unfortunately, after Oct 31st it will cost $49 to start up, and you will not get your first month free, so signup now to save yourself $49.