One of the biggest sports names in marketing, Beckham's brand was recently estimated to be worth 200 million pounds ($334.5 million) by the Observer newspaper.
"He's an interesting phenomenon," said sports public relations expert Karen Osborne at London-based agency Cohn and Wolfe.
"There are not many people in sports who can be paralleled, people that literally step out of the sports fame into general fame and will go down in history."
Beckham, 28, has been at the centre of transfer speculation for weeks and has been linked with a move away from Manchester United to Barcelona, AC Milan or Real Madrid.
As Beckham's soccer star has risen the player has popped up on billboards and television screens around the world.
Adidas pay him to wear their boots, he has worn clothes for Marks and Spencer, his talked-about hair was the platform for Brylcreem and he has donned designer sunglasses for Police.
ADVERTISERS' DREAM
But just how has the quiet footballer who joined Manchester United as a schoolboy become such a hot property off the pitch?
"He is incredibly photogenic and he has a lot of fans," said Osborne, whose clients include Coca-Cola and England's Premier League.
"People have a compassion for him because he has not always been a hero through and through. When he cried, when he had problems, when he was sent off, people certainly felt compassion for him," she added.
Beckham's name could fulfil every advertiser's dream -- guaranteed media coverage. That has been enhanced by his glamorous life with pop star wife Victoria, a former Spice Girl.
Beckham's universal iconic appeal was certainly what pushed Vodafone to hook up with the footballer, the British mobile phone giant said.
"We use David as a lifestyle icon. He does not appear in our advertising dressed in
"The great appeal about David is it is universal across the age range. He's liked by children and grandmas and he is liked by football fans and non-football fans," said Caldwell, whose firm are halfway through a two-year contract with Beckham.
Vodafone also use Beckham to advertise in Japan, where the midfielder's fame soared during the 2002 World Cup.
It seems that Beckham cannot lose. He could move anywhere in the world and the advertisers would flock behind him.
"We would clearly look at whether we could use David in our advertising in whichever country he ended up in," said Caldwell.
MARKETING APPEAL
British media reports say Beckham earns in excess of 90,000 pounds a week at Manchester United and off-field activities earn him around 10 million pounds more a year.
Some might see photo shoots and advertising tours as a distraction but the English Premier League said it would generally not take issue with players cashing in on their teams' high profiles.
"If anything it is part and parcel of being in a successful team in a successful league," said a spokesman.
"Players like David Beckham, like Michael Owen, like Alan Shearer, people who do have massive marketing appeal, do help draw people into the game," he added.
Cohn and Wolfe's Osborne said the "clothes horse" had a good 10 years in the public eye yet if his brand-savvy wife Victoria continued to manage their happy marriage with the media moguls.
"It's not just a whim that he decides to plait his hair, or a whim that he wants to wear a skirt. I think it is quite cleverly personally manipulated," said Osborne.
"His hair will probably go black next if he moves to Italy."
Beckham's agents complained this week that the player was being used as a "political pawn" in the campaign for the club's presidential elections but all the transfer speculation can only supplement the designer dresser's spending money.
"They are certainly capitalising on the peak interest in him now, the money he is supposed to be making from this Asian tour will be enough to set him up for life," said Osborne.