I love the Direct Talk (aka MotoTalk) feature. I use it on a Nextel i576. When Nextel went out of business, it was easy to pick them up for about $40 each on eBay and other places. They do require a Nextel SIM Card, but you can buy 100 of those on eBay for almost nothing. They don't need to be activated to use Direct Talk.
They are similar to the Motorola DTR and DLR series radios, in that they use 900 Mhz FHSS on the ISM band. The Nextel phones use 700 mw, which is slightly lower power than the 1 Watt that the DLR/DTR Radios use. I've read that they are not compatible with the Motorola DTR and DLR series, though.
Given how old the batteries on my i576s are, I'm starting to consider some kind of alternative, like the DLR and DTR radios.