Man if my line went down using my mobile to get on the net would be the last think I'd consider, you are an addict Dave!
With a decent plan - and the need for mobility - I can see the need, and have one myself. I use my phone as a wifi hotspot and (wirelessly) hook up either my laptop or my Iconia depending on what or how much I need to do.
Being able to do that from anywhere is a bonus, for me.