The Live 8 text contest has attracted 1.5 million entries within hours, as people try to win tickets for next month's London show.
Coldplay will be performing in London's Hyde Park
More than 150,000 tickets have been made available in the text competition.
Entrants aged 16 and over must send the answer to a multiple choice question to 84599 before midnight on Sunday.
The question is: Which city is nearest to the G8 summit in July? A) Berlin, B) Moscow, C) Edinburgh. Entries are £1.50 plus the usual text message charge.
Five gigs are being held around the world on 2 July to highlight world poverty. Entries can also be posted.
It will feature Coldplay, Keane, Sir Elton John, U2, REM and The Cure among others.
HOW TO ENTER
Answer the question: Which city is nearest to the G8 summit in July? A) Berlin, B) Moscow, C) Edinburgh
Text A, B or C to 84599 between 8am Monday and midnight Sunday 12 June
Calls cost £1.50 (plus operators' standard network rate) and can only be sent from the UK and Channel Islands
Competitors must be at least 16
Answers can also be sent on a postcard to Live 8 Ticket Competition, PO Box 4026, Leamington Spa, CV31 9AZ by 1300 BST on Friday.
There is no limit to the number of times people can enter the competition. After 12 June a computer will randomly select 72,500 people with the correct answer, to each receive a pair of tickets.
A Live 8 spokesman said nearly 1.5 million entries had been received by 1700 BST on Monday.
He said: "Bob's delighted. I've just told him and he said: 'It's great'."
He added that anyone texting between now and midnight on 12 June would have an equal chance.
Organisers said the first £1.6m raised from the text competition will go to The Prince's Trust which is sharing a proportion of the income with Help a London Child.
The rest, after paying the costs of the concert, will go to the Band Aid Trust.
On the same day as the Hyde Park gig there will be concerts in Philadelphia, Paris, Berlin and Rome. Details of how to attend these shows have not yet been announced.
The gigs, which are part of the Make Poverty History campaign, come four days before leaders of the world's richest countries meet in Gleneagles, Perthshire, for the G8 summit.
Organiser Bob Geldof then wants people to head for Edinburgh in time for an anti-poverty "party" on 6 July which he is calling "The Long Walk to Justice".
On Monday he launched another part of the campaign - entitled Sail 8 - to encourage British sailors to cross the Channel to bring people back to join the anti-poverty walk.
His spokeswoman said British yachtswoman Ellen MacArthur also intended to take part in a mass flotilla of boats.
Launching Live 8 last week, Geldof said: "The G8 leaders have it within their power to alter history.
"They will only have the will to do so if millions of people show them that enough is enough."
Some economists are sceptical that the aims of the Make Poverty History campaign would help the people it is targeted at.
Those who do not win tickets will be able to watch the London concert on screens in the centre of cities across the UK including Birmingham, Hull, Liverpool, Manchester, Plymouth, Belfast, Leeds and Wrexham. A plan to show the concert in Portsmouth has been cancelled.
The concerts are the brainchild of Geldof, Richard Curtis, Midge Ure and promoter Harvey Goldsmith.