Pros
Culture! Not for everyone, but having worked in multiple industries and large companies, this is by far the best one I've been in. It's also a land of opportunity for process improvements. Transitioning from a fast growth to a more mature company requires a lot of review of prior efforts to come up with new and better ways of doing things. One of the onboarding sessions has everyone take a quick personality profile and the majority of employees in my session liked change and more social environments, which is why T-Mobile has the culture it does.
Cons
Team together doesn't always apply, many groups are more interested in maintaining their processes than working together. Management doesn't force the issue many times and let's the stress foster.