By Caroline Karobia BBC News, Nairobi

Mobile phone base stations have sprung up all over Kenya

If you want to find a growth industry in Kenya, the mobile phone market is a good place to start.

Less than a decade after the mobile was introduced in the continent, the number of people connected has soared - and now there could be as many as ten mobile phone subscribers for every landline.

There are millions of mobile phone users in Kenya now, a far cry from the 15,000 there were six years ago when prices were sky-high.

Now, though, Safaricom - one of the country's privately-owned operators - has almost five million subscribers, while its main competitor, Celtel, has close to three million.

Competition has intensified, and the companies are constantly introducing new services and at lower rates to gain - and keep - subscribers.

01 Regional boost

This year alone, Safaricom has launched five new services for its consumers.

For Celtel, the count is seven - the latest being what the firm calls its "One Network".

The aim, Celtel marketing director Anne Othoro says, is to provide Africa's first borderless mobile network in a region where, traditionally, trading and family relationships have crossed national borders.

"One network is about one region," she says.

Mobiles are hailed as economic saviours

"Between Uganda, Tanzania and Kenya there has been a lot of trading going on but we still have our boundaries.

What we've done... is to break down those boundaries in terms of the network."

In practical terms, Celtel says that Kenyan subscribers will be able to travel to each of the two neighbouring countries and continue to use their phones - without changing the SIM card inside the phone and while paying that country's domestic rate rather than a much higher roaming charge.

The company says it can do this because it runs its own network in the two countries, as well as 11 others across Africa.

Following suit

Celtel's initiative has spurred an instant response from its larger competitor.

"We can do and we will do exactly the same as they are doing," says Michael Joseph, Safaricom's chief executive officer.

"If we have an agreement with MTN Uganda and Vodacom of Tanzania, we can exactly the same thing as what Celtel has done."

The increased competitive pressure is coming not only from the two dominant carriers.

"You've seen there are a number of these talks of other companies coming into our field," Mr Joseph says.

So there is probably still plenty of room for innovation yet to come - and there are still about 30 million Kenyans to sell phones to.