Why did the Sprint/Nextel 'push to talk' phone lose interest? - Quora
Nextel i355
Nextel i880 - Review 2007 - PCMag UK
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... :
Motorola's Ruggedised Phone
93 Motorola Nextel Photos and Premium High Res Pictures - Getty Images