UK consumers experienced problems with two million of the 18 million mobile phones sold last year, according to a survey by consumer watchdog Which?.
Around 70 per cent of problems occurred in the first six months after purchase, and over a quarter of the 5,000 people surveyed said they were unhappy with the way their problem had been handled.
Which? said that a whopping one in three handsets supplied by '3' developed a problem within 12 months, but acknowledged that this might be because of "teething problems" with the new 3G technology.
The mobile operator maintained that it was unfair to compare its service, which offers relatively complex video downloads and video calls, with the more established mobile networks.
It also complained that the research was unrepresentative because it included only 50 '3' customers out of a total of one million.
The Which? report did not make a distinction between a handset fault and a network fault because it is still the responsibility of retailers to resolve the problem under the Sale of Goods and Services Act.
Problems included faulty keypads, failure to connect to the network and problems with storing phone book entries.
Vodafone, which had 15 per cent of customers reporting a fault, said in a statement: "We have a rigorous approval system before a handset is accepted onto our network or sold through our stores.
"The research does not indicate what the faults actually were or if they were resolved to the customer's satisfaction. At the end of the day a phone that doesn't work doesn't make money for us, so it is in our interest to solve any problems."
Which? has set up a model complaint letter to help people who believe they are not getting the right response from their retailer, stressing that retailers are legally liable for any faults within the first six months of use.
A separate report published in May found that there are now more mobile phones than people in the UK.
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