Apparently there is going to be an iPad/iPhone Borderlands coming out very soon. As in sometime this month (October in case you haven't left your basement in a while).
It's called Borderlands Legends and features the four original Borderlands characters and their powers, weapons, a "strategic cover system", a "fight for your life" mode, randomized missions, and of course "in-game cash".
Whether the "in-game cash" means we will also have to pay with "real-life cash" we simply don't know. Have to find out when it releases I suppose.