It's no accident that Apple chose a yellow icon for its walkie-talkie feature. I dug out my old (2002ish) Nextel with PTT (push to talk). It was all the rage back then... :
1 Motorola Nextel i576 Walkie Talkie w/ Direct Talk and Enhanced Privacy GRADE A | eBay
TOAN MAGAZINE — Throwback Thursday: Nextel/Boost Mobile Chirp...
Chirp Chirp* NEXTEL | When Phones Were Fun | For a few years in America, it was tough to go a day in public without hearing a distinctive electronic “chirp.” By 2004,
95 Motorola Nextel Photos & High Res Pictures - Getty Images
The TTABlog®: Precedential No. 24: TTAB Finds Another Motorola "Chirp" Sound Unregistrable