Avenue A/Razorfish will handle the web build and architecture, while VCCP will be responsible for building brand strategy and online advertising.
The agencies will be briefed to bring O2.co.uk in line with the rest of the company's branding. The site will launch at the end of July, and will be backed by a range of on- and offline advertising initiatives.
Andrew Pattison, the head of online operations and delivery at O2, said: "Joining forces made the case for VCCP and Avenue A/Razorfish extremely compelling."