The service allows consumers to buy items such as mobile ringtones, horoscopes and share advice online for as little as a few pence, without having to register their credit card details each time.
Customers register their details once on btclickandbuy.com or through one of the retailers.
From next March, the service will be expanded so that purchases will be chargeable on BT customers' phone bills, according to BT click&buy business director Helen Davis.
The company is also planning to leverage its sponsorships of charities Childline, Comic Relief and Children in Need by offering a 'click&give' option, encouraging people who prefer to make small donations.
BT click&buy is also being promoted on the landing page of BT Broadband.Davis said it would not be promoted in a dedicated ad campaign because of the complexity of explaining the concept.