EE, Orange and T-Mobile customers around the UK are reporting that their 3G service has deteriorated since the company launched its 4G network at the end of October.
Problems connecting to the internet via 3G have been reported in Manchester, Preston, East London, Hull, as well as parts of Cornwall, Scotland and the North West, leading to speculation that the company is deliberately throttling its 3G service to encourage customers to upgrade to 4G.
"Since service changed from Orange to #EE the 3G speeds have gone rubbish, what I [sic] doing about it!!" tweeted @DomSowler from Oldham.
"3G coverage on my iPhone4 has become effectively nonexistent recently. It's becoming more&more frustrating as tmobile used to be great," said @StephenJConroy from Hamilton, Scotland.
"Beyond SICK of @EE - this 3G connection makes me want to cry! It used to be fine... #conspiracytobuy4G" added @LizzieCougz from East Yorkshire.
EE told Techworld that the company is aware of a few isolated issues, but denied that those issues had anything to do with the rollout of its 4G network.
"There is a potential, when upgrading to 4G, that there is an impact on 2G. In the process of switching on the base station there may be a temporary outage of an hour or two," a spokesperson said.
"However, there should be no impact on 3G. This is not a nation-wide issue."
Orange previously suffered an outage at the beginning of November - just days after the launch of EE's 4G service. (EE's network runs over Orange and T-Mobile's combined infrastructure).
The company confirmed that "some customers could not access 2G and 3G data" for a short period of time, but that this issue was quickly rectified. Calls and texts were unaffected.
Meanwhile, the company is being investigated by Trading Standards following a complaint that its advertisements are "grossly misleading".
Earlier this month, a man from Plymouth complained to Trading Standards over a poster in his local EE store which claimed that "4G is here," even though the nearest 4G signal to Plymouth is 120 miles away in Bristol.
EE said that this was an isolated error, and the poster has since been removed. The company added that it won't be advertising 4G overtly in those stores that are not in 4G covered cities.
EE's 4G service is currently available in Bristol, Birmingham, Cardiff, Edinburgh, Glasgow, Leeds, Liverpool, London, Manchester, Sheffield and Southampton. The service will be available in a further five cities before Christmas, with more cities and rural locations planned for 2013.