The website appears to be down. Having said that...
I may not be remembering this correctly, but didn't most mobile phones also have a walkie-talkie feature built-in in the 90's ? I don't think any have that now.
I'm not sure if I'd feel the same today, but back in the early 2000s, that was such a great feature. I was pretty sad when our company decided to move from Nextel over to a traditional carrier without push-to-talk.
It was super useful to track people down when you were trying to coordinate. I remember on 9/11 in NYC, my nextel phone was the only one that was working in washington square park. I had a line of people waiting to use it to call loved ones to let them know they were okay.
As a high schooler who only had Nextel phones for the cool factor, I will never forget the constant anxiety in the back of my mind that I'd have the phone off mute and one of my friends would chirp me when I'm around my parents with something I'd rather they not hear.
Ha! I can imagine that. We occasionally had that issue, but mostly my group of friends and coworkers shared some basic rules for using the push-to-talk. E.g. no pushing the button and then just saying something, unless you were already talking back and forth; the first chirp was always an empty chirp. If the other party was available, then they could respond. Stuff like that. I can see that with some raunchy high school friends it could get pretty awkward.
I remember Nextel phones having that cool feature (and a distinctive chirp sound)...but don't recall other phones having that...THen again, i always did have cheapy phones back in the day. It is surprising why walkie-talkie-like features aren't more popular nowadays...Then again, maybe messaging apps might fit enough of the original need.
from https://en.wikipedia.org/wiki/Nextel_Communications
"Nextel's iDEN network offered a then unique push-to-talk "walkie-talkie" feature in addition to direct-dialed voice calls."