The homelessness charity Crisis is to receive £387,000 donated by customers of a mobile network who were affected by this month's data outage.
Ash Schofield, chief executive of Giffgaff, said last week it was setting up a goodwill fund for customers hit by the O2 outage on 6 December.
Giffgaff buys services from O2, so its customers were among the 30 million affected.
They were offered the chance to either take a share of the fund as credit or donate their portion to charity.
Schofield posted on Giffgaff's community forum yesterday that the fund would be worth £1m.
Of this, £613,000 would be credited to customers and £387,000 would go to Crisis.
He added that the donation meant "more people will be able to access companionship and essential services over Christmas at Crisis centres across the country, as well as support their efforts to end homelessness throughout the year".
A Giffgaff spokeswoman said the company had not supported Crisis before, but its work chimed with Giffgaff's sense of community. She said the company wanted to support a charity that had an impact at this time of year.
"Crisis seemed a great fit given that it’s the national charity for the homeless, offering essential services to people over Christmas and all year round," she said.
A Crisis spokesman said the money had been donated as unrestricted funds and would be spent on its Christmas appeal and as general funds.
According to accounts filed with the Charity Commission, Crisis's income was £35.2m in the financial year ending 30 June 2017, up from £29.5m the previous year.