Lineone switched on its free unmetered internet service on Friday, but three days later many customers are still waiting to be connected.
Customers who had pre-registered for the service, being run with telecom provider Quip, may have to wait until later this week before they can actually go online.
Quip said it had received "tens of thousands" of pre-registrations for the service, but refused to specify how many people had been caught in the backlog. It said customers are being connected on a 'first come, first served' basis.
The service offers free unmetered internet calls all day, every day, with no introductory fee or annual charge. Subscribers need to register with Quip, purchase a £20 box that redirects calls to Lineone and spend £5 a month on voice calls.
On Friday the companies announced that the service was live and available to users. But several customers told vnunet.com on Monday that despite pre-registering with Lineone several weeks ago, they were still waiting to be connected.
Simon Lubin, marketing director at Quip, said: "Other companies have tried to process everyone in one go and have suffered problems. We have brought in extra bodies to cope with the registering and will contact people in batches to clear the backlog."
The companies will contact all customers that have pre-registered, advising them when they can expect to get online. "Users will be sent an email with details for full registration, and once credit card details have been verified the online process is instantaneous. It is our target to get everyone processed by Wednesday or Thursday this week," Lubin said.
Lubin could not confirm how many customers had registered or how many were still waiting to get online but said the company was getting through the numbers very quickly.
Last month, Telewest compensated users of its unmetered internet deal for the poor quality of the service. Customers of Telewest's £10-a-month Surfunlimited service received a £10 credit on their account after the company's modems and telephone exchanges became overburdened by demand for the unmetered service.
US company AltaVista said it would strictly control the number of users it signs up to its own unmetered service. Initial registration will be limited to just 500,000 customers.
Connexin drops out of Ofcom auction due to start next week
SwiftKey users now send two billion emoji every week
Recruitment plans are 'most ambitious ever', claims Openreach HR director Kevin Brady
Samsung's under-the-hood improvements separate the S9 from the pack when it comes to the display