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... :
History and Stuff
Nextel makes leap into 21st century
Nextel Launches the Motorola i850 Camera Phone
Throwback Tech: Old school cell phones - Electronic Products
2x motorola nextel direct talk walkie talkie cellphones with GPS & retro games www.iuu.org.tr