THOUSANDS of nine-digit pager owners will have to change the first four digits of their numbers in October as the telephone system moves to accommodate growing telecommunications services. Every one of the estimated 1.1 million pagers would change to eight digits from the current seven or nine, and all will start with a '7', the Office of the Telecommunications Authority said yesterday to remind the public. Seven-digit operator-assisted pagers will simply add a '7', while the first two digits of the nine-digit secretarial or automatic pager numbers will be replaced by a '7'. But that has led to about 30,000 of these pager numbers being duplicated among companies. Those owners will have the first four digits of their numbers changed, according to Alex Cheung King-shek, vice-chairman of the Hong Kong Radio Paging Association. For instance, Mr Cheung's company, Telecom Services Limited, has nine-digit pagers which begin '1113'. Under the plan, the first two digits should be replaced with a '7'. But four other companies have pagers starting '713', so they drew lots. 'We have had to change to 747 - like the [old] Cathay number,' he said. 'That's a bit confusing. Of course it's inconvenient but it had to be done,' he said. The change was needed because numbers beginning with '1' were being reserved for directory services under the numbering plan for deregulation and expansion, said the authority's senior administration officer Eliza Yau Kwai-chong. Mr Cheung estimated as many as 300,000 customers had nine-digit pagers, of which about 30 per cent would be affected. Many companies - including his - were offering discounts for advance fee payment to avoid losing customers who might prefer other companies' numbers. Association representative on the authority's numbering committee Alex Pang Kam-wing said there would be a 'dual access' period in October and November when both numbers would work and a messaging system running through December and January to tell all callers the new number of the pager.