Don't want or need a POTS line, certainly not for $40 per month, but its not really about the $$ in that regard - I run Asterisk. Why? I like not having people being able to just dial straight through. My server presents a menu, which is only really navigable if you actually already know who you want to talk to).
Not sure how much data you use but for example: The price difference between Telstraclear Lightspeed 60GB (naked no phone) at $95 and Telecom Total Home Broadband 60GB (includes land line) at $105 is $10 (not $40).
So assuming you never used the land line, would you pay $10 more a month for not being limited by Telstraclears upstream TCP issues?
I would also look at Snap and maybe even specialist ISP's like Unleash who do offer naked ADSL, even offering VDSL2 now too.