Squeezed by wireless giants, have the regional mobile carriers just given up?

Back in the mid-2000s, there was a pretty vibrant community of mid-sized regional mobile providers in the US. Alltel ruled over the rural providers with 12 million subscribers and a bigger coverage area than even the nationwide carriers, while multiple operators — from Dobson Communications to Centennial Wireless — boasted millions of subscribers and were forces with which to be reckoned in their corners of the US. No more. In the last five years all of those carriers and many more have been gobbled up by the national carriers. And the Big 4 have only come back to the operator buffet for more. Have the smaller operators just given up on the mobile business?