The Department of Justice has started an informal review of the exclusive arrangements that limit handsets such as Apple’s iPhone to particular wireless communications companies, according to people familiar with the matter.

The inquiry follows consolidation in the US wireless industry that has left four operators accounting for more than 90 per cent of the country’s wireless subscribers. This has left them with the market power to carve out exclusive deals with makers of the most popular handsets, making it hard for smaller rivals to compete and leading to higher prices for mobile services, according to rivals.