One of the surprising things about the mobile broadband market in 4G and 5G is how important cellular voice has remained. Not in revenue terms – most mobile operators include voice virtually for free in their service bundles, and usage has declined in the face of Internet voice applications. But abandoning voice altogether has proved far more difficult than many expected in 4G, and the number of examples of successful data-only mobile services is vanishingly small. Operators had to undergo the challenging migration to Voice over LTE (VoLTE), as the circuit-switched 2G and 3G networks were replaced with IP architectures (or live with the inefficiencies of circuit-switched fallback). They have tried to add value to voice services with adoption…