Yahoo and BT are extending their partnership to offer UK consumers the option of making telephone calls over Yahoo's messaging product, the companies announced today.

The integrated call management product, called Yahoo Messenger with BT Communicator, will include VoIP (voice over Internet protocol) services like PC-to-phone calling, internet call waiting and directory lookup, bundled with instant messaging features, according to Yahoo spokeswoman Sue Jackson.

The service will allow users to easily switch from instant message conversations to a telephone conversation, according to Jackson.

Yahoo Messenger with BT Communicator will be made available for trial in May, and the product will be formally launched later in the year, though she declined to specify a date.

The companies are in the midst of running trials of the product with both Yahoo and BT customers, according to Jackson. Quality has been a consistently problematic issue for VoIP services in general.

Telephone calls made through the Yahoo/BT product will be billed directly to the customer's home phone bill at normal toll-call rates.

BT Communicator will be integrated into all Yahoo Messenger clients distributed in the UK and additional features will be added to the product in the future.