Pros
T-Mobile is a company where decisions are typically made for the correct reasons; if ideas can be demonstrated to be good, they are pursued. If ideas can be demonstrated to be bad, they are not pursued. The challenge, of course, is getting this information to decision-makers through all the layers of upper management; but when presented information, virtually all senior leadership acts logically and rationally, without pursuing personal agendas.
Cons
In many ways, the company's values are used as a crutch to perpetuate incompetence. Cronyism is a real problem in some parts of the company, and some of the entrenched leadership protects its position by pushing more competent people out of the company before those people can become threats - under the guise of maintaining and protecting the company's values.