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... :
Nextel Motorola i530 Walkie Talkie Black Boost Mobile Flip Phone | eBay
Sprint Pulls Plug on Nextel iDEN Network Tonight | PCMag
Motorola i860 - Wikipedia
Motorola i560 Rugged Nextel Phone Announced - ecoustics.com