The launch of "free" broadband deals has prompted a downturn in customer satisfaction levels, a report claims.
A survey of more than 11,000 customers shows falling prices have not always led to better service.
Most providers are failing to match the growth in customer numbers with improved customer services and investment in technology, according to the uSwitch customer satisfaction report.
Customers are now more likely to get both their home phone lines and broadband from the same company.
This has pushed up the likelihood of speaking to customer services on a more regular basis, the report says.
But overall customer satisfaction levels have dropped by nine per cent among broadband users and four per cent among home phone users compared to a previous uSwitch survey six months earlier.
Consumer trust in their suppliers is at an "all time low", the report says.
The biggest cause of concern is whether suppliers are making sure customers are on the best available deal.
Steve Weller, head of communications services at uSwitch.com, said the advent of low-cost broadband deals had pushed up subscriber numbers by nearly 650,000 since March.
"However, it’s disappointing to see that the majority of providers are failing to accompany the growth in customers numbers by sufficient growth in customer service operations and the required investment in their technology to ensure that they are looking after customer needs in an acceptable manner," he said.
Virgin.net was the broadband provider with which customers were most satisfied. Some 85 per cent of its customers who were questioned expressed satisfaction.
The uSwitch.com survey put Telewest and Tiscali second and third at 83 per cent and 80 per cent respectively. Orange came joint bottom with TalkTalk at 70 per cent.
Of the home phone providers, Tiscali came top with a customer satisfaction rating of 81 per cent. TalkTalk and Telewest both got 80 per cent, followed by BT at 72 per cent and ntl at 70 per cent.
Chris Robertson, technology, media & telecommunications (TMT) partner at Deloitte in Birmingham, said: "The 21st Century appears to be an increasingly benevolent era, particularly within the context of telecommunications products and services. Consumers and businesses are being offered an ever widening range of goods, for a ticket prize of zero.
"This is thanks to a subsidy, often worth hundreds of pounds. Subsidies were a powerful tool during the high-growth phase of the industry, but may have become an expensive and uncomfortable legacy.
"The cost of this free offer can often include the obligatory purchase of another service (or services); a charge for the privilege of being released from the free service; the cost of calling a premium rate, technical support hotline when the modem that was provided for free proves a nightmare to install, or stops working.
"There are already numerous examples of free offers turning into public-relations nightmares, and companies must carefully consider the implications of marketing ‘free’. Not only are consumer groups likely to keep a close eye on the small print associated with free offers, but also competition authorities and regulators may well pay increasing attention."