Mobile operators’ battle against over-the-top voice and messaging apps is a game of one step forward, five steps back. Ahead of the MNOs’ showcase in Barcelona next week, the portents were not good for the former bedrock of their business. In the face of OTT success, the South Korean operators were forced to shut down their Joyn services – based on the GSMA’s big hope for preserving cellco differentiation, RCS (Rich Communication Services). And if the Korean giants – which have embraced OTT themselves more effectively than most – can’t succeed, there’s little hope for many of their counterparts elsewhere. The other technology which, optimists say, can enable mobile operators to offer something distinct from the messaging apps, is VoLTE…