Brazen director Emma Thornley said: 'We intend to be making headlines for Phones4U - to help make it the consumer's number one choice for mobile phones.'
A four-strong account team headed by Brazen owner and director Nina Wheeler and Thornley will be responsible for the high-street brand's PR work. They will report to Julian Neal, Phones4U marketing director.
Phones4U continues to retain fellow northern agency Ptarmigan, to look after the firm's sponsorship of Birmingham City Football Club.
Neal said: 'Phones4U is a rapidly expanding company and we see marketing and comms as a critical tool for ensuring this growth continues.'
Phones4U is the UK's fastest growing mobile phone retailer. It operates a national chain of more than 220 stores and is the retail arm of the Caudwell Group of Companies.
Founded in 1986 by John Caudwell, the group operates in five countries and employs more than 2,000 staff worldwide. The group was founded in 1986, and reached a turnover of more than £1 bn in 2000.
Brazen's appointment is part of a major marketing investment by the retail giant, which had a record-breaking 2001, seeing Phones4U cement its position in the mobile phone retail market by opening a further 160 stores.