
Clarke will assume responsibility for sales and marketing activities at Carphone Warehouse's TalkTalk Group.
She was responsible for the launch of TalkTalk in 2003, and was marketing director of Carphone Warehouse before her move to the Best Buy retail division six months ago.
Carphone Warehouse still plans to open its first Best Buy-branded big-box stores in the UK later this year.
A spokesman confirmed that Pagliari is leaving following the integration of Carphone Warehouse's AOL and TalkTalk broadband teams. His plans are not yet known.
Pagliari joined AOL UK in 2003, before it was bought by Carphone Warehouse, and has headed marketing for the TalkTalk and AOL broadband brands since September.