Microsoft Australia and Telstra have joined forces to trial IP telephony via MSN Messenger and Windows Messenger.
The initial four-month trial is targetting 3000 of Telstra's broadband customers.
The companies said other features such as interactive services and unified messaging may be included.
To use the Telstra Internet Calling Trial service, users need to have MSN or Windows Messenger installed on their PC and open a pre-paid credit card account with Telstra.
To make a call, users simply log on, open the program, chose the option 'make a phone call' and enter the number.
Stuart Lee, executive director voice and commercial, Telstra Retail, said: "Internet calling is not the same as ordinary voice telephony. It is an Internet application that interfaces with our telephone network and this creates new challenges, both in terms of technical delivery and customer requirements."
The statement said prices for the service will be "competitive" with current standard mobile, long-distance and international calling rates.
The trial, which is limited to outbound calls only, will end in August 2002.