Don't provide a landline number, and say you are ordering a new service, not a service migration. If you can't get the ISP to confirm this is what is happening, cancel the order with them. I was able to do this with Zen when I went to FTTP, though they wouldn't be on my recommended list for other reasons now.
Once you have the new service up and running and are happy with it, transfer the voice number to AAISP VOIP. This will trigger a cease on your copper services usually.
Note that the transfer of the number to AAISP is a bit one way, as AAISP don't have number porting agreements with many providers. This means in future if you wanted to port the "landline" number to another provider you may not be able to (or may have to port it to a supported provider first). The AAISP VOIP service is reasonably priced enough though that you're perhaps unlikely to need to.