The news breaks as it also emerges that WCRS is to lose the £5 million First Direct account. The HSBC-owned banking brand will be handled by the eventual winner of HSBC's current global agency consolidation.
Phones4U called a pitch six months ago as part of plans to change its marketing strategy. It is looking to move away from price-led advertising and instead promote its customer service.
WCRS has been briefed to deliver a campaign including television, print, point of sale and direct mail work. The agency's first executions will be produced towards the end of the spring.
Paul Hamburger, the marketing director at Phones4U, said: "The appointment of WCRS as our creative agency is part of a new marketing team and strategy that will help to make Phones4U the market leader."
Separately, WCRS is understood to be in the final stages of its £20 million management buyout, led by the agency's chairman, Robin Wight, from its Havas parent.