Carphone's acquisition of IPTV service Tiscali in July increased customer numbers to 4.1m, a rise of 48% year-on-year.
Excluding Tiscali, the telecoms firm added 124,000 net new customers in the first half of the year.
Chief Executive Charles Dunstone said that the brand's TalkTalk Group and Best Buy Europe had traded well in the first half of the financial year.
"We expect continued strong customer growth in the second half," he added.
Revenues at TalkTalk were up 15% overall to £631m despite a difficult consumer climate, offsetting declines in voice-only and internet dial-up users.
Carphone Warehouse signed up to a £7 million three-year sponsorship of X-Factor with ITV in June 2007.