Pros
Good work life balance (flexible and home working), though it depends on what team you're in within head office.
Cons
Appallingly low salaries, huge cronyism the only way to progress professionally. HR processes totally divorced from employee experiences. Financial backing uncertainty for anything but 4G, with money likely to be promised and then pulled away several times during any year - whether by finance, or your own director trying to book Opex as revenue and hide what a poor job he's made of profitability, even when it's a drop in the ocean. Many senior level people seemingly woefully out of their depths and therefore showing blatant favouritism to yes men, or people who will do large swathes of their jobs for them so they can coast. Actually, that's hit the nail on the head: most of senior leadership content to coast through the rest of their careers without ever taking risks or innovating. Frequent redundancies that are purely tactical in nature (make EE appear profitable to the owning companies, France Telecom and Deutsche Telekom).