There still exists
AirPeak Communications.
They are a small iDEN provider in Riverside county, CA with coverage into the Mexico border.
Sprint murdered iDEN in June 2013. The coveted 860MHz spectrum is now known as band 26 "extended CLR" and Sprint has EVDO and LTE there.
Southern Linc is alot like a high ranking White house guy that speaks in duality. One press release says they plan to implement LTE as a data solution alongside iDEN, the other suggests that LTE will replace iDEN. Their selection of WAVE suggests the latter being the case.
Being that MSI no longer is developing any new iDEN handsets, and most FNE is in extended support phase, it's safe to say LTE will replace SoCo's iDEN and be another LTE player on band 26 along side Sprint.
The state loves Southern LINC. The real question is: with First Net coming, how will SoCo and the state respond? SoCo has a robust network and backhaul for their iDEN, if they do the same thing for LTE, it will be hard to beat and whatever cartel (AT&T) gets the First Net buildout will have tough competition that is well entrenched with many government users.