Apple introduced the new Walkie-Talkie feature in the new Apple Watch Series 4 with watchOS 5 in June during their WWDC 2018 Keynote. Apple began describing the use of a personal transmitter system or walkie-talkie like technology back in 2011. Apple was granted a patent for this kind of walkie-talkie technology in 2014. Today the U.S. and Hong Kong Patent and Trademark Offices published Apple's application for the figurative trademark for Walkie-Talkie as presented below.
Application In-Part for Walkie-Talkie Figurative Trademark
Apple's Walkie-Talkie Specimen Provided for in Filing
Apple filed their trademark under International Class 009 for hardware in the US and Hong Kong with Class 14 added in Hong Kong to cover "Horological and chromatic instruments and watches" to cover Apple Watch.
Apple Support: Walkie-Talkie How-to Video