London is set for an extra 10 million landline phone numbers to accommodate growing demand by new homes and offices.
Telecoms regulator Ofcom announced it is introducing a new 0204 number range to help Londoners "stay connected".
While there are 30 million numbers using (020)3, (020)7 and (020)8, fewer than 500,000 remain to be handed out.
Ofcom said these will be used up within a year as it distributes 30,000 London numbers each week.
Needed for broadband
UK customers spend 44 billion minutes making landline calls every year, Ofcom said, and despite usage being in decline, landlines are still needed for fixed-line broadband.
In 1958 London was allocated the code 01, which remained until 1990 when it was replaced by two codes - 071 for inner London numbers, and 081 for outer London, Ofcom said.
Five years later, all UK area codes gained a "1" after the "0" to make it clear it was a landline number, and the capital's codes changed to 0171 and 0181, it added.
In 2000, the UK's phone numbers were reorganised through the "Big Number Change" when London was given a single area code of 020 and the inner and outer London divide was removed, the regulator said.
The regulator will start accepting applications for (020)4 numbers from October and expects the new numbers to start being allocated to customers from December.