Basically, it's a bit like sending an e-mail as it uses the internet. When you're online you can call any number, whether it's a home phone in Hobart or a mobile in Melbourne, and receive calls from anyone, anywhere in the world. You can get a standard Australian phone number specific to your Freshtel internet phone account.
To make and receive calls you will need to have your computer on or have an internet telephone adapter (ATA) and be connected to the internet. However, don't worry if your computer is off or you are not connected to the internet because just like a mobile, callers can leave a message on your voicemail which you can pick up at a later time, free or charge. While you're on your internet phone you'll still be able to use the internet and other applications on your computer.