Found this when looking to move my home cable connection from Optus to Telstra. Clicked through a link from "My Account" (I have a Telstra mobile already), but the link included above appears to work just fine. Conditions simply say "$100 Welcome credit for new customers".
If you're looking to move to Telstra to take advantage of the fancy new cable speeds and unlimited plans then why not get $100 off too??
I went for the $99/month Entertainment bundle and my welcome credit was automatically applied to the connection fee of $99. The $100 welcome credit looked like it also applied to the $69 and $129 per month bundles too.
Rep on chat confirmed speeds of 50/5. No other discounts offered.
Edit: Screenshot
https://ibb.co/covzOc
You would have to be one of a very, very limited subset of people in Australia with access to both Optus and Telstra cable in your street.