Nextel phones have never had FRS/GMRS radios built into them, nor did they ever work without cellular connectivity. The "push to talk" feature is called Direct Connect and works with some Sprint phones now. Direct Connect has always required cellular connectivity, despite the name.

I like the idea of mesh connectivity between phones and it looks like Beartooth and goTenna are making moves in that direction. I also like the idea of broadcast radio receivers built-in to smartphones. Right now there are some bluetooth devices that purport to do that, but I've never tried one.