In addition to the unlimited $29.99 data plan, you would also need a $29.99 tethering plan, so it would cost you $60 a month - and the connection would not be as good as your DSL. And we use our DSL to connect to a router and have several laptops and desktops using our DSL, which would not work with a tethered connection. My advice - skip the tethering and keep the DSL.
as soon as you teather the plan is no longer unlimited. it goes to 5gb a month
is this enough usage for you?