A US court began hearing evidence in a long-awaited case brought by 14 attorney generals, which could derail the proposed big money merger of Sprint and T-Mobile US.

The legal action is being brought by representatives from 13 states and the District of Columbia, led by New York State attorney general Letitia James and her California counterpart Xavier Becerra.

During the first day of the case at a federal court in Manhattan, executives from Sprint and T-Mobile parent company Deutsche Telekom (DT) were called to give evidence.

LightShed Partners analyst Walter Piecyk, who was regularly tweeting from day one of the hearing, stated the target is to conclude the trial on 20 December.

The attorney generals are attempting to prove the merger would have a negative impact on competition, while Sprint, T-Mobile US and their parent companies maintain the deal would be beneficial for consumers.

A number of concessions and promises have already been offered in an attempt to woo detractors.

In the weeks running up to the case, and following a number of vows by outgoing T-Mobile US CEO John Legere, four states dropped out of the legal action.

The $26 billion deal was announced in April 2018 and was originally due to be completed by the end of H1 2019. The Federal Communications Commission and Department of Justice have already passed the deal, the latter following a promise to divest assets to Dish Network.