More than 150,000 customers are stuck in the queue waiting to sign up to NTL's unmetered internet service, the company has revealed.

NTL today said that at the end of last week it had connected only 190,000 customers and taken details from, but not signed up, a further 150,000. NTL said the remaining customers would be connected by the end of September.

Launched in April, the ntlworld service offers unmetered internet access included in the price of phone rental for NTL customers. For non-NTL customers, they must purchase a line adaptor for £10 and spend a minimum of £10 a month on voice calls.

NTL said it is now capable of registering 20,000 customers per week. A spokeswoman for NTL said its gradual approach to getting customers on to the service has been "very sensible" and has avoided problems that other ISPs have suffered.

"We needed to be sensible in signing customers up, to protect the network and ensure a quality of service to existing users. The service itself has been very successful and feedback has been extremely positive. We are the only operator who is staying with the free access model," she said.

Many customers have complained to vnunet.com that they have waited months for the registration disks to arrive. The UK advertising watchdog has received 154 complaints about the ntlworld service, from customers who felt the ad campaign was misleading because it did not warn about delays.

The Advertising Standards Authority (ASA) said the complaints have reached a record level for an ad which does not fall into the taste and decency category. It said the complaints are currently under consideration by its council, with a decision unlikely to be made until at least next month.

The NTL spokeswoman said that while she was unable to comment until the ASA makes its decision, the company believes it acted responsibility. "We work closely with the ASA and have carried out all its requests. We acted responsibly and removed advertising as quickly as possible when we realised it was causing a problem. We think the ASA recognises that."

NTL said it will resume an "aggressive promotion of the service in September".