An extra 15.7 million eight-digit mobile-phone numbers may be released by next year, meaning Hongkongers might soon have numbers starting with the ominous digit four, as well as seven and lucky number eight. The Office of the Communications Authority launched a two-month public consultation on the matter yesterday, and proposed using new prefixes and recycling old numbers to generate extra mobile-phone numbers. Among the five measures proposed, the watchdog said reallocating numbers starting with four was the most effective, as 5.6 million numbers could be released to meet demand for 42 months. That idea, however, was not welcomed by operators or subscribers because the number "four" in Cantonese sounds similar to the word for death. So seriously is the tradition taken that some developers exclude floors with the number from buildings. "How could we promote and sell those numbers? Four is a taboo in Chinese culture," one of the operators said. The authority's spokesman admitted operators had complained about the idea, but said the number should be used. "Nowadays people use smartphones and don't memorise phone numbers anyway. So what's the big deal with digit four?" He said numbers starting with four could also be used for pre-paid SIM cards and data-only service plans. The watchdog also proposed reallocating two-thirds of existing pager numbers and reallocating some numbers starting with 70 to 73 for mobile services. Reallocating vacant numbers starting with 81 to 83 was also proposed. Those two measures could release 3.2 million and 980,000 phone numbers respectively. According to the authority, Hongkongers register new mobiles at a rate of 145,000 a month, and 16.7 million phone numbers are now registered. That means for every Hongkonger, there are more than two mobiles in service. The authority said there were 4.97 million numbers available for mobiles, but these could be used up as early as November 2018 because of the city's insatiable appetite for smartphones Migration to nine-digit numbering is not under discussion, as the move could cost the city HK$1 billion. "Operators would have to upgrade networks and databases. Business sectors would have to update equipment," the spokesman said. "It might be a future plan when all eight-digit numbers run out. But definitely not now." The watchdog said a total of 15.7 million subscriber numbers would become available if all five measures were implemented, which could extend the lifespan of the eight-digit numbering plan by around 10 years, to September 2028. The eight-digit numbering has been in use since 1995.