The ISP, one of the biggest in the UK, announced it was reviewing its creative account in June, having worked with Mortimer Whittaker O'Sullivan (MWO) for five years.
MWO will continue to work for the ISP on a project basis and is involved in AOL's current campaign.
AOL's past advertising has featured virtual character Connie, but she is now being replaced by brand images and messages demonstrating the breadth and depth of AOL's service.
Grey fought off competition from TBWA\London, WCRS and Euro RSCG Wnek Gosper Partners for the task. It will continue its brand strategy and is expected to break a major campaign early next year, when the ISP launches the latest version of its access software.
AOL is stepping up its advertising spend to promote its content and software services and keep up with arch rivals BT and Freeserve. Both have ploughed millions of pounds into advertising their broadband services in recent months.
According to Sharon Lang, AOL UK's vice-president of marketing, its advertising will continue to promote its broadband and narrowband services, but broadband "will get a significant airing in the coming months".
"It's important that we keep the consumer up to date with all the services and products that we are offering, so we will communicate the benefits of both broadband and narrowband," she said.
Despite speculation that AOL was considering putting its media business up for review, Lang denied this, insisting that it would continue to work with incumbent Vizeum.
AOL's planned increase in adspend follows last week's announcement from America Online that it plans to scale up its UK advertising, with the budget increasing from $115m (£68m) to $275m (£162m) next year.