EasyMobile

No phones (and certainly no phone subsidies) and no owned towers = EasyMobile.  According to this post on Boing Boing, EasyMobile service will consist of you purchasing a SIM card and finding your own phone.  Furthermore, EasyMobile is simply leasing tower capacity from other carriers and reselling it under their brand-name (much like Virgin Mobile does here in the US with Sprint PCS)  This comes from the same people that brought the UK EasyJet, the low-cost airline that is strikingly similar to Southwest.  Service launches in December.