By the BBC's Dan Isaacs Lagos

Africa's most populous nation, Nigeria, is in the grip of mobile phone fever.

Investors have long recognised the growth potential for mobile phones on a continent where existing landline networks are limited.

You see people in public transportation, private vehicles, restaurants, water closets. They're talking 24 hours a day.

Ladi Akeredolu-Ale

But nowhere is the potential greater than in Nigeria. The state-owned telecoms company, Nitel, has only 400,000 lines for a population of 120 million - one of the lowest connectivity rates in the world.

Since two private companies with GSM licences started operating in Nigeria last year, sales of mobile phones have soared.

Pent-up demand

Econet, from Zimbabwe, and MTN, from South Africa, have provided 600,000 lines since they began operation in August 2001- already substantially more than all of the landlines in the country.

Gridlock, Lagos-style

MTN's boss in Nigeria, Adrian Wood, says its the fastest take-off of any country, and that the target is more than 10 million users within 5 years.

Mobile phones are particularly welcome in Nigeria's commercial capital, Lagos, a bustling city with the unenviable reputation of having the worst traffic jams in the world.

More than 12 million people live here, and sometimes it seems as if all of them are on the move at the same time.

Until last year, a trader who wanted urgently to talk to a supplier across this seething mass of a city had to get there herself.

Now communications are much easier for those who can afford a mobile phone.

Ubiquitous

"Everybody wants one," says Ladi Akeredolu-Ale, a local television journalist. "I suppose the only thing standing in the way of most people is the cost."

Everybody wants one

"You see people in public transportation, private vehicles, restaurants, water closets," he adds. "They're talking 24 hours a day."

The two competing phone companies are desperately trying to keep up with demand.

It's not just the wealthy and fashion conscious that have taken up the challenge.

On the hunt for a mobile user in a busy Lagos market, I found Mabel Ogunleye, selling crates of soft drinks and dealing with a customer on the phone.

"It has really enlarged my business," Mabel says.

Out of control

Clearly, starved of effective communication for so long, Nigerians can take the mobile phone craze too far.

Take your pick - if you can afford one

"I have a colleague who has 4 phones and a personal assistant who has no job other than to carry those phones from place to place to answer all of them," says journalist Ladi Akeredolu-Ale.

And some unwanted callers sometimes get the brush-off, Nigerian style.

"Hi this is Ladi," Akeredolu-Ale says into his phone. "I'm not available right now. I'm out partying, so why don't you just leave your number and when I get over my hangover I'll give you a call."