Originally Posted by
CatJo
Definitely try them out on the $30 prepaid plan, but it's important to use an LTE Band 12 phone as a lot of the new network expansion uses this 700MHz spectrum. We'll know next week if the new iPhone 6S support it (very likely it will, the current iPhone 6 does not); in the meantime, get something like an LG Leon ($50 on sale from T-Mobile right now, often at Best Buy for under $70) which has excellent support for all T-Mobile bands and great cellular radios to boot.
Why should OP have to purchase anything? As stated up-thread, OP can call the T-Mobile business department and probably get setup with a free trail.