The mobile network announced the HD voice service, which uses the speech bandwidth of 50-7000Hz compared to the current narrowband speech codec of 300-3400 Hz, in January this year.
Orange says it "delivers excellent audio quality to mobile calls" and revealed it was already working with handset manufacturers and devices supporting HD Voice, which will be rolled out throughout this year.
"High-definition voice represents a huge advance for the customer experience, and a great leap forward for the mobile industry. We are delighted to be at the forefront in bringing this innovation to the UK public," said Tom Alexander, chief executive of Everything Everywhere, the company formed when the mobile network merged with T-Mobile, earlier this year
A limited number of consumers and businesses have been selected for the trial.
The service, which has already been launched by Orange in Moldova, is expected to be rolled-out across the country later this year.