Sprint's CFO, Tarek Robbiati, was recently noted stating that 'unlimited' is unlikely to be a "sustainable proposition" in the future. Robbiati was noted making the comments during an investors meeting where the topic was briefly touched upon. While Robbiati made no suggestion that the unlimited battle is due to come to an end anytime soon, Robbiati did make it clear that in terms of the bigger picture, or the "longer run", it is unlikely that companies will be able to continue battling on the unlimited front, indefinitely.
The reason for the comments is that Robbiati explains that there is the issue of capacity and the ability to maintain and provide for an ever-increased need for capacity. Due to this, Robbiati suggests that as time goes on, the cost associated with unlimited will inevitably have to go up accordingly. Robbiati was making the comments as part of a wider approach to explaining that Sprint is in a better position than others to combat this long-term effect of unlimited, due to its spectrum portfolio. One which means that, according to Robbiati, Sprint will be able to increase capacity at a more affordable rate than others. Robbiati further drove home this point, but noting that the 'unlimited race' is not quite the race to the bottom that it currently seems to be. Instead, Robbiati argues that it is more of a "race toward building capacity" and one which means that the more capacity a carrier has, the greater its ability to continue building out that capacity without incurring (or passing on) costs will be. Essentially, Sprint is in a better long term position to accommodate unlimited at an affordable rate, than others.
In either case, it is clear that 'unlimited' is unlikely to reach any major hurdles in the near future and will continue to be the big selling point that it has been of late. This has become a key battleground recently with all of the major carriers, including Verizon, bringing their own interpretation of unlimited to the table. The race to the bottom that Robbiati speaks of, is relevant to how carriers seem to be looking to win custom for the particular unlimited flavor by including added-value aspects, like for instance, HD streaming. So while the long term race to building out capacity filters on, it is likely that a race to offer the most value-laden unlimited will also continue.