If you want to know what ISP’s are on your exchange and what plans they offer, visit http://whirlpool.net.au/ and enter your phone number in the top right hand corner.
This site also has active forums where you’ll get opinions on a range of ISP’s.
If you are ever moving business premises, make sure you understand the internet connection that will be available to you prior to signing the contract. It is my understanding that land developers are responsible for putting the cable down, and they are cutting corners. I have several clients who can only access dial-up connections living in new developments.