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... :
Direct PTT - The Nextel T320 is the full package. This model is a Smart- Radio with PTT & 2-Way Manage your entire fleet from your palm with full GPS Tracking and Mapping.
Merger narrows cell phone field / Sprint-Nextel deal leaves four major wireless services in U.S.
Nextel Mobile | StartEngine
Nextel i300 AT&T | Anker Wireless
Nextel makes leap into 21st century
Remember When Phones Were Walkie Talkies? - YouTube
Nextel i95cl review: Nextel i95cl - CNET
Motorola / Nextel I355 Iden Cell 2-way Radio for sale online | eBay
18 Things You Once Said That Would Make No Sense To Today's Kids | Boost mobile, Walkie talkie, Best mobile phone