Late 19th century (in an earlier sense). Apparently partly from radio- + -phone, and partly (especially in later use) from radio- + -phone. With sense 1 compare French radiophone, and slightly earlier radiophony.
Definition of radiophone in US English:
radiophone
nounˈreɪdɪə(ʊ)fəʊn
Radio-telephone.
Origin
Late 19th century (in an earlier sense). Apparently partly from radio- + -phone, and partly (especially in later use) from radio- + -phone. With sense 1 compare French radiophone, and slightly earlier radiophony.