Belfast and its surrounding area is the best in the UK for overall mobile network performance, according to research.
Research company RootMetrics tested the performance of the four main operators in the UK's 16 most populated areas.
London ranked fourth from the bottom, with only Bristol, Hull and Cardiff getting lower overall scores.
But RootMetrics said all the areas surveyed had improved over the past few years.
Newcastle and Glasgow were both singled out for improved network performance, thanks in part to increased data reliability and speed.
The research focused on six categories:
Belfast, Manchester, and Liverpool took the top three places in four of the six categories.
As well as being ranked best overall, Belfast was found to be best for text performance, data performance and speed.
Manchester was the best performing in terms of network reliability and call performance.
Of the 16 cities RootMetrics studied, Cardiff got the lowest score.
RootMetrics' research showed that data speeds in the area were getting faster, but the networks' performance in the other categories was largely unchanged from the first half of 2016.
The research covered not just the named cities but their surrounding areas.
The region covered by the London data, for example, stretches "from Maidenhead to Southend-on-Sea, and from Tunbridge Wells to Cambridge", according to Scott Stonham, general manager for RootMetrics Europe.
"There's a high level of transient demand from people travelling through the area, which is difficult to plan for, and the bigger the area the harder that is," he said.
"With the numbers of people and the area covered, we get quite a wide spectrum of performance. London as a city is much better."
RootMetrics said that the improved mobile performance in Newcastle was the result of faster download speeds, data reliability, and fewer blocked and dropped calls on all the networks.
In Glasgow, the researchers found "significant improvements" to both the speed and reliability of data services.
RootMetrics overall performance ranking