The competition watchdog has provisionally approved BT's £12.5 billion merger with mobile phone firm EE.
Telecoms giant BT announced in February that it had agreed to acquire EE with the deal expected to be completed next March.
Rivals had questioned whether a deal between the two would weaken competition in the market, but both firms claimed the merger would enable them to invest billions more into Britain's digital economy.
In provisionally clearing the deal, the Competition and Markets Authority (CMA) said the companies "operated largely in separate areas".
John Wotton, chairman of the CMA inquiry, said: "The group does not provisionally believe that, in a dynamic and evolving sector, it is more likely than not that BT/EE will be able to use its position to damage competition or the interests of consumers.
"We recognise that this is a merger which is important to many consumers and businesses. We have heard a number of concerns from competitors. After a detailed investigation, our provisional view is that these concerns will not translate into a competition problem in practice."