BC Partners has bought PHONES 4U after months of talks.
The fund takes control of the firm from Providence Equity Partners – a price has not been revealed.
Providence has been mulling a sale since September after a number of firms signalled their interest in the company.
Providence bought Phones 4U from founder John Caudwell in 2006.
A sale would result in a second windfall for Caudwell. He kept a small stake in the business after raking in £1.5bn from selling his empire four years ago.