you have been ABLE to do that for as long as I can remember (I've kept the same number since 2005 now on all the major networks. I only didn't keep my number prior to that because it was a work provided contract) but depending on which you were dealing with would put up a number of different obstacles when you contact them to make the process as painful as possible (to keep you as a customer... THREE I'm looking at you!) so the new automated SMS process introduced in July is a welcome addition