The company, which runs T-Mobile and Orange brands in the UK, said its total customer base shrunk by 1.4 per cent to 27.5m from the previous year.
Everything Everywhere, which was created by a tie-up of France Telecom' Orange UK and Deutsche Telekom's -Mobile UK in 2010, reported turnover of £1.7bn, down 4.3 per cent compared with a year-earlier.
Without the impact of regulatory cuts on Mobile Termination Rates, the underlying revenue was up by 0.6 per cent.
The company has also made good progress in signing up contract customers, and selling more expensive smartphones.
It said 85 per cent of its new contract customers opted for smartphones such as Apple's iPhone, Research in Motion's BlackBerry and HTC phones in the third quarter.
Everything Everywhere, which has focussed on contract customers who are more profitable for operators than pay-as-you-go users, said it had added a net 185,000 contract customers in the third quarter - the same figure as in the year-earlier period.
The joint venture lost a net 227,000 prepay customers.
Service revenue which reflects the ongoing amount generated by customers, excluding the impact of regulatory measures, was up by 3.8 percent or down 1.9 per cent when the measures were included.
"The success we've had adding nearly 900,000 postpaid customers in the last year is helping to drive underlying service revenue growth," said Chief Executive Olaf Swantee, who replaced Tom Alexander on 1 September.
The company, which was formed to help its parents compete in the cut-throat UK market, has retained both the Orange and the T-Mobile brands but it has also trialled new stores under the Everything Everywhere name.
Everything Everyhere said it was making good progress in cutting costs and said it was on track to make at least £3.5bn worth of synergy savings by 2014.
The joint venture, which operates from more than 700 retail stores across the UK, competes with Telefonica's O2, Vodafone and Hutchison Whampoa's 3 UK.