EE and Vodafone have come bottom of a UK survey ranking mobile operators for customer experience.
The two operators were measured on their Net Promoter Score by vendor Satmetrix, which developed the metric along with Bain & Company and Fred Reichheld.
For the survey, customers are asked one key loyalty question: How likely is it that you would recommend [Company X or Brand X] to a friend or colleague?
They were then rated as promoters, passives, and detractors.
Detractors are described as being unhappy customers who can damage your brand and impede growth through negative word-of-mouth.
EE finished bottom behind Vodafone, with scores of -7 and -1 respectively.
Tesco Mobile was the highest rated telco with a score of +38; more than half of the respondents said they would recommend the company.
The MVNO came third in the overall table, which was headed by bank First Direct (+73) and Nationwide Building Society (+43).
Three got a score of +16, O2 +9 and Virgin Mobile +7.
Eleven thousand people took part in the survey in January and February.
In addition to NPS, they rated each brand on various aspects of customer experience, including product or service features, customer service and overall value.
Tesco Mobile scored particularly well on ease of use and the cost of calls and texts.
However, EE customers pointed to difficulty in getting help, while Vodafone suffered from not treating customers fairly and mobile internet speeds.
Brendan Rocks, Head of Data Science at Satmetrix, commented: "The Net Promoter leaders are more likely to enjoy high customer retention, lower customer acquisition costs, and ultimately benefit from more sustainable growth.”