I asked the same question before I sign up with TPG and I found out that they don't offer 'Internet' only plan for NBN. So even though you don't use the home phone, it's stil part of the plan. ( Any NBN Plan )
Hi @JohnHolley, no you're definitely not penalised if you only want to use the internet part of your Internet and Home Phone bundle.
Although it is a bundled internet and phone service, you can choose not to plug in a handset. I suggest choosing an NBN plan with Pay As You Go calls. At least you have the option to use the home phone if you ever need it.
What plan are you thinking?
Edit: just noticed you said you are thinking about the NBN SL Bundle which does have PAYG calls, good choice!