O'Brien picked up the phone and made a call. Within weeks, the 35m deal was done and Digicel was born.

O'Brien had built Esat from scratch and sold it to British Telecom in 2000 for 1.7bn so he knew the mobile telephone market. Even in his wildest dreams, however, he could not have anticipated that in just six years Digicel would be worth so much and he would personally make a profit of more than 600m by taking total control of the business. Digicel has propelled 49-year-old Denis O'Brien into the billionaire league. In the Caribbean, its brand is as recognisable as McDonald's or Coca Cola.

Now operating in 22 countries with five million customers and 3,400 staff, Digicel is a remarkable success story but the banks tried to talk him out of coming here. Setting up in Jamaica was one of his biggest risks. Most investors looking at the statistics for the island of 2.7 million people would have run a mile. With more than 1,300 murders a year, it is one of the most dangerous places in the world.

Besides the number of people killing each other, the economic data didn't look too promising, with high unemployment, inflation and low growth. What O'Brien realised was that, although the country looked like a basket case on paper, there was a huge amount of cash in the hands of ordinary citizens.

One of the main reasons for this is drugs. It is estimated 40% of GDP is not reported because of drugs, money laundering or underground trade. He knew if he could just get a network up and running, the people would flock to use it and would have the cash to spend.

Most people had never owned a phone before Digicel's arrival, with the cheapest handset costing over $500. Local people despised Cable and Wireless because they took profits out of the country but neglected to improve service, price or coverage. O'Brien has discounted phones, introduced cheap calls and made them accessible to everybody.

In just six years, the company signed up 1.7 million customers and has 70% of the market. The huge level of interest took the company by surprise, so they began expanding across the Caribbean with similar spectacular results. Digicel's success in Jamaica has been surpassed in Haiti, one of the world's poorest countries. In just 14 months since its launch, the company has signed up 1.6m customers. Denis O'Brien says he "has never seen a market like it". Every day for two weeks there were six-hour queues outside Digicel stores to buy phones.

'Fairy godmother' Keith Collister is a renowned Jamaican economist who regularly contributes articles to the Jamaican Gleaner, one of the oldest newspapers in the world. He has followed Digicel's progress since their arrival. "Digicel are very well regarded here and people have been very welcoming towards them because of the way they took on Cable and Wireless.

They had planned to be number one from day one."

Denis O'Brien keeps a low profile in the region and relies on his core Irish management team to run the business. Because of the expansion of the company, O'Brien is only in Jamaica once a month for board meetings. Also on the board of directors is his close friend, Fianna Fail fixer PJ Mara.

The secret of O'Brien's success in the Caribbean is the loyalty he has built up among his customers.

He set out to make his company an integral part of the community and Digicel is the biggest corporate donor to charities in Jamaica. He set up the Digicel Foundation and has spent millions of euro on a range of charitable projects. When Hurricane Ivan devastated Jamaica in 2004, O'Brien approved a 25m donation to help rebuild the island. From providing Christmas dinners to the poor to committing to building 20 schools in Haiti, O'Brien and Digicel are involved in literally every good cause in the Caribbean.

As well as donating money to charity, the company spends a phenomenal amount of money on marketing. You cannot walk down the street in Kingston without being bombarded by the red and green Digicel logo. Sponsorship is another huge element of the company's marketing strategy and it sponsors dozens of sporting, cultural and music events. The president of the region's football confederation, Concacaf, refers to the company as a "fairy godmother" for all the cash it has ploughed into sport.

The only time over the last six years that there was any controversy surrounding O'Brien's company was in February 2005. Digicel's marketing manager Richard Nowell accompanied the West Indies cricket team on a tour of Australia. It cost Digicel 15m to sponsor the team and Nowell was less than impressed with the professionalism of the athletes. In an internal report leaked to a newspaper, he wrote that some players had scored more women's phone numbers than runs and he had heard women's voices in players' rooms in the early hours of the morning before one match. He referred to some of the team as a "terrorist group" because they refused to do media interviews and he said Digicel wasn't getting any value for money. Denis O'Brien said he wouldn't comment on the report until there was an internal review.

O'Brien's staff do not have a bad word to say about him and many of them have benefited from the success of Digicel because of generous share options and bonuses.

The best ever Digicel Jamaica's CEO David Hall has a lot of admiration for his boss:

"I have worked with Denis for 10 years now and he's the best I've ever worked with and I'm not just saying that. He's unbelievable and you have to admire what he's achieved. His energy levels are unbelievable. You'd be in a meeting with him and he'd be taking one call after another. He's very bright and approachable and all the senior managers have his mobile number and you don't get in trouble for ringing him and his advice is practically always spot on. That's not to say that he won't give you a kick in the backside if it's needed".

Hall, who is from Waterford and has been in Jamaica for six years, thinks it is the challenge to achieve what people do not think is possible that motivates O'Brien. "Let's be honest. He has enough money to do him for the rest of his life but he likes to do the undoable."

There are around 100 Irish employees based around the Caribbean islands, with the majority operating in specialised highskilled areas such as engineering, computing or finance. Most have come here over the past two years with the majority being under 30.

A core group of people located to Jamaica when Digicel launched in 2001, but most of that group have moved on. Many staff members previously worked for O'Brien in Esat. He demands his people put in long hours but there is time for socialising and the Irish are popular around the island.

Limerick-born Lawrence Hickey is chief financial officer of the Digicel group and is one of O'Brien's most trusted lieutenants.

He has been in Jamaica five years.

"I love it here. The work is ferocious and we move at such a fast pace. It's been a real rollercoaster for us. The Irish and Caribbean workers are very proud of Digicel.

Although it's an Irish company, locals see it as a Caribbean company. The social life here is very good. There are lots of work functions to attend and a lot of dinners and balls and most of the Irish staff would go out on Friday and Saturday nights. They work hard and play hard, " says Hickey.

The Irish staff have set up a soccer league and even played a GAA match against locals in the Cayman Islands two years ago. Keith Collister believes that because of Digicel's Irish connection the company was destined to do well. "Jamaican and Irish people are not dissimilar in terms of style. They both like a drink, a party and like to sing and dance. There is a natural cultural affinity."

Hundreds of Irish fans were in Jamaica for the recent cricket World Cup and Digicel helped to look after the Irish team. When they shocked the tournament by progressing to the second round, Denis O'Brien made a quiet donation of 150,000 to help pay their expenses. Digicel sponsors the main horseracing event of the year and one of the most popular races is the annual Digicel Irish Jamaican Stakes. There are streets in Kingston named after the four Irish provinces and Irish has even found its way into the local Patwan language. The Patwan word for a jumper is 'geansai'.

David Hall has seen many of his Irish staff meet Jamaican women and says, "A lot of them will be here forever."

If Digicel is like a family, then its Irish staff are O'Brien's favourite child. When he flies into the country on Digicel business, he has been known to see an Irish staff member in the lift and stop for a chat. This often ends with him asking when they were last home and more often than not he tells them to go and get some clothes so they can catch a lift in his private jet back to Ireland later that day. Every Irish worker gets at least two return flights home paid by the company each year.

It is not just the Irish that are looked after. A few months ago a Jamaican worker discovered she had cancer. She is a popular staff member and the whole organisation was devastated. O'Brien got to hear about it and had a quiet word with the woman who is only in her early 30s. He told her to get the best medical treatment she could and he would pick up the bill. Digicel staff say that is typical of Denis O'Brien and that he takes a great personal interest in his people. He also enjoys a good gossip and likes to be kept up to speed about all the mischief and shenanigans around the office.

David Hall says O'Brien is very compassionate when it comes to people. "We like to pull at his heartstrings. We'll bring him to a Digicel Foundation event and once he sees what we're doing, he usually decides to put more money into the project. He has a very soft side and is great fun and a fantastic storyteller. But he works you hard and you have to work around the clock, that's the reality. If you are not fully committed, then there's no place for you in Digicel and I'm sure that's the same in all his businesses."

Runaway success O'Brien is not impressed with Jamaica's high crime levels and constantly refers to it when he speaks in the country. This has put pressure on the government and police to clean up their acts and the murder rate has fallen over the last few years. When the company first came to the island, a local gang set fire to a telephone site in an attempt to extort money.

Over 2m worth of damage was caused but the police were told not to investigate. Instead representatives of the company went in to the local community under the orders of Denis O'Brien and told them in no uncertain terms that if anything like that happened again then Digicel would leave the island. That was the first and last incident.

Collister believes Jamaica holds a special place in the heart of Denis O'Brien. "I think he genuinely cares about Jamaica because it was his first investment in the Caribbean and has been so successful for him.

"He probably has a special fondness for here and Jamaica is certainly fond of him. With the possible exception of Cable and Wireless, it is hard to get anybody to say anything bad about Denis O'Brien or Digicel. It's been an enormous success story."