T-Mobile is the brand name used by the mobile communications subsidiaries of the German telecommunications company Deutsche Telekom AG. The brand is active in Austria (under the subsidiary T-Mobile Austria), the Czech Republic (T-Mobile Czech Republic), the Netherlands (T-Mobile Nederland), Poland (T-Mobile Polska), and the United States (T-Mobile US). The name was previously used by subsidiaries in other countries, including Albania (now Telekom Albania), Croatia (now Hrvatski Telekom), Germany (now Deutsche Telekom), Hungary (now Magyar Telekom), Macedonia (now Makedonski Telekom), Montenegro (now Crnogorski Telekom), the United Kingdom (now EE Limited), Romania (now Telekom Romania), and Slovakia (now Slovak Telekom).
Deutsche Telekom previously owned the holding company T-Mobile International AG for its mobile communications subsidiaries. From 2003 to 2007 T-Mobile International was one of Deutsche Telekom's segments beside the segments of 'Broadband/Fixnet', 'Business Customers' and 'Group HQ and Shared Services'. T-Mobile International AG then lost relevance when Deutsche Telekom transformed its structure to adopt a regional setup (Germany, Europe, USA) in 2009 by combining its previously separated fixed and mobile subsidiaries to form integrated local businesses.
When T-Mobile International AG existed, the holding company was based in Bonn, Germany and its subsidiaries operated GSM, UMTS and LTE-based cellular networks in Europe, the United States, Puerto Rico and the U.S. Virgin Islands. The company had financial stakes in mobile operators in both Central and Eastern Europe. Globally, T-Mobile International's subsidiaries had a combined total of approximately 230 million subscribers. T-Mobile International was the world's thirteenth-largest mobile-phone service provider by subscribers and the fourth-largest multinational after the UK's Vodafone, India's Airtel, and Spain's Telefónica. Wikipedia