Carphone Warehouse is to launch a new mobile phone service, which will run through Vodafone's network.
Carphone Warehouse and Vodafone are working together again
To be called Talkmobile, it will run alongside Carphone's existing services, Fresh and TalkTalk Mobile, which operate through T-Mobile's network.
The deal with Vodafone comes as a surprise, as a year ago Vodafone said Carphone would no longer be able to sell its mobile phone contracts.
A sign of rapprochement between the two firms, Carphone's shares rose 3.6%.
Carphone Warehouse will continue not to sell Vodafone's mobile phone contracts.
Renting network space
Talkmobile will be a pay monthly service based around a nine-month contract.
It will operate by renting excess network capacity from Vodafone, the same as Fresh and TalkTalk Mobile do through T-Mobile.
Virgin Mobile has a similar arrangement with T-Mobile, and such services are known as mobile virtual network operators or MVNOs.
Carphone is the UK's largest mobile phone retailer.