Last month the FCC ruled AT&T be conditionally cleared to offer wireless calling while a replacement teletypewriter (TTC) system (named RTT) be developed. This aging system is traditionally required to be supported in order for a carrier to offer wireless calling, but the FCC, in response to pressure, has decided to bend its own rules a bit in the name of progress.
Following its decision regarding AT&T, the FCC invited "requests from similarly situated providers seeking a similar waiver of the TTY requirements." Verizon responded to this with a petition late last week, requesting it be granted the same waiver.
In other words, Verizon customers may soon be able to make wireless calls with no strings attached. Currently you must be on iOS 9 and use the Verizon app, but if allowed, this would mean the ability to make the calls on Android as well, and no app would be required regardless of OS.
The purpose of wireless calling, if it's not obvious, is to provide one with the ability to make calls when the primary network is weak or non-existent.