Japan's mobile phone service providers are spending heavily as they brace themselves for the introduction of number portability, local media sources say.

From 24 October, mobile phone users will be able to keep their existing numbers when they switch to a new service provider. Millions of mobile customers are expected to switch. 

Operators are adding mobile phone base stations in areas they previously considered to have 100 per cent coverage, the Asahi Shimbun reports, fearing that subscribers whose phones have poor coverage will switch to another firm. 

Softbank announced last month that it will spend $4bn adding 23,000 new 3G base stations within a year, and NTT DoCoMo is to spend a similar sum. 

New handsets are expected from all of Japan's major mobile phone service providers. KDDI, for example, last week announced 12 new phone models simultaneously. The new phones are made by eight different manufacturers. 

Mobile phones in Japan are often licensed exclusively from the manufacturer and are available only from a single service provider. The providers use phone features as a means of attracting subscribers.

Moving to a new provider will not be completely effortless for customers, however. They will have to pay approximately $45 each time they switch, with about half going to the old operator and half to the new.

But subsidies will help defray customers' costs. Mobile operator Vodafone KK, recently bought out by Softbank, is offering about $20 in credit to customers who apply to switch to its network during the next few weeks.