On this chart from the Spectrum Ownership Analysis Tool, you can see the PCS spectrum in Chicago and St. Louis that Sprint acquired along with the subscribers and network. Thus it was clear to see that USCellular's AWS(B) and AWS(E) spectrum was no longer needed.
It clearly makes sense for T-Mobile to acquire this spectrum as indicated in the chart below. In St Louis, T-Mobile will increase their LTE Channel size from 10MHz to 25MHz and in Kansas City, T-Mobile will increase from 10MHz to 15MHz. The chart also highlights the important spectrum position that Leap hold in the AWS band which both T-Mobile and Verizon would desire to add to their portfolio.