The £15 billion merger between Vodafone and Three could increase prices for the 85 million mobile phone customers in the UK, rival telecom firm BT has warned. It also cautioned about “poorer network quality and reduced incentives to invest.” The explosive intervention was made in a written report filed with the UK Competition and Markets Authority (CMA), which is in the process of investigating the proposed merger between Three and Vodafone. It’s worth noting that BT, which competes directly with Three and Vodafone, received approval from the CMA to acquire EE for £12.5 billion in January 2016…