The company said it gained new 77,000 subscribers in the period, compared with City predictions for an increase of some 41,000.
Carphone also said its customer churn rate improved as the quarter progressed after it boosted its customer retention efforts.
The company ended September with a total broadband customer base of 4.1 million, including 1.3 million from the recently acquired Tiscali UK. Carphone became the UK's largest residential broadband supplier after the acquisition.
In Carphone's retail arm, which is now part of a joint venture with US electronics retailer Best Buy, connections grew 2% to 3.17 million year-on-year.
Carphone said it would meet expectations across its group operation for the year to the end of March.