The study examined customer care via telephone with a live service representative, automated response systems, walk-in help in retail stories and online assistance. It assigned index scores to each type of interaction.
The study found that customers that speak with a service rep over the phone had an average satisfaction index score of 109. The average index score for in-store help was 102. The average index score was 85 for automated response systems and 75 for those who sought help online, the company said.
The results pose a serious challenge for wireless operators, according to J.D. Power.
"As more companies encourage customers to contact Internet and computer-based customer service programs to save operating costs, they run the risk of increasing churn (when a customer switches carriers) as the number of contacts needed to resolve a customer complaint or issue rises," Kirk Parsons, senior director of wireless services at J.D. Power and Associates, said in a statement.
The study ranked T-Mobile highest among U.S. carriers for its customer service and assistance. T-Mobile received a satisfaction index score of 108. Verizon Wireless, Nextel and ALLTEL also ranked above the average score of 100, the company said.