As the cellular market matures, many mobile phone operators worry about how to squeeze extra revenue out of their customers when subscriber growth rates start to slow down.

Those looking for inspiration should visit Italy where Omnitel, the country's second largest operator, has launched a bewildering range of information and entertainment services that can be accessed via a voice portal, as well as using more conventional methods such as SMS and Wap (Wireless application protocol).

The portal, Omnitel 2000, is claimed to represents the world's largest deployment of natural speech recognition in the telecommunications industry. It gets around 250,000 calls a day although on peak days the volume of calls can double.

The voice portal is based on a natural language speech recognition system, called SpeechMania, from Philips Speech Processing, the speech technology division of Philips Electronics.

SpeechMania, which runs on the Windows NT operating system, is designed for telephony applications and aims to allow callers to obtain information over the phone using natural language. The Dutch and Swedish railways use SpeechMania for their speech-enabled train information and reservation systems.

The Omnitel installation is much more ambitious, however, both in the scale of the system and the number of services supported. Because of this, Philips had to expand its Italian language specialists and set up training courses for the new members of both Philips and Omnitel.

Before the portal went live in late 1999, the operator had just over 7m customers. Today, Omnitel has almost 16m users and, like many operators, is keen to find new ways to generate revenue from its customers beyond simply encouraging them to make more telephone calls.

Omnitel is majority owned by Vodafone, the world's biggest mobile phone group and it has quickly made its mark in the cellular industry.

Nevertheless, when it set out to break Telecom Italia's monopoly on cellular communications in 1995, things did not go so well and sales fell significantly below expectations.

To find out where it was going wrong, Omnitel conducted extensive marketing research that identified untapped market segments in Italy. It developed a new service plan, Libero, which, as its name suggests, sought to liberate customers from the complexities of existing tariff structures.

This ability to find new opportunities has made Omnitel a text-book case in innovation for the telecommunications sector - Harvard Business School uses Omnitel as a case study in its marketing courses.

The flair for innovation has continued with Omnitel 2000, a portal that provides Omnitel customers with a diverse range of services.

The portal allows customers to access a suite of more than 300 databases, including restaurant guides, directories and additional types of information services offered by Omnitel.

Some of the more unusual recent offerings on Omnitel 2000 have included a service to listen to songs and participate in polls for the San Remo song festival, which is a national institution in Italy, and a similar service for fans of Il Grande Fratello - Italy's version of the Big Brother TV programme that has taken much of Europe and now the US by storm.

More prosaically, Omnitel 2000 recently launched an m-commerce service for its 400,000 Wap users. By tapping on the keys of their Wap phone, these users can order products ranging from PC peripherals and cellular phones to wine.

Many of the services offered on the Omnitel 2000 portal can be accessed in several ways: via the website (www.omnitel2000.it), via Wap phones, using SMS messages - useful for receiving news flashes for example - or using the voice portal.

Omnitel customers need only key "2000" on their mobile phone to reach the voice portal which they navigate by listening to the prompts and speaking in a natural fashion.

Omnitel has also made the voice portal accessible to customers of other mobile operators as well as those using a standard fixed phone. For these users, the service is accessed using a regular telephone number and is charged as a national call.

Voice portals have acquired a mixed reputation because they can be difficult for consumers to navigate. Nevertheless, Omnitel claims its voice portal is easy to use because it takes advantage of a feature in the Philips technology that not only understands what the caller says but also intuitively anticipates where a caller's inquiry may be heading.

Callers can immediately jump to a particular service by pronouncing its name, or navigate through the hundreds of services offered via the Omnitel 2000 platform in a natural manner.

After a year of operation of the voice portal, Omnitel analysed the usage made of the services and the results were revealing. For example, the original idea was to use the voice portal to offer an extensive range of services - around 150 were originally defined. However, the usage data revealed that just seven services generated 90 per cent of usage.

Another surprising result was that 60 per cent of callers froze on their first call and did not know what to say. Italians are known for many things but not usually for being short of words.