Three years ago everyone was green with envy at Nextel's push-to-talk (PTT) service. Network vendors, handset makers, and carriers were all eager to duplicate Nextel's success. Everyone was ready for PTT to explode and they all predicted the cash cow was just around the corner. Then... nothing happened.Actually, a few things happened. First, Nextel was acquired by Sprint. In the early stages of the merger, Nextel's legacy clients didn't get the service they were accustomed to and there were issues. But, that's all in the past and things now seem to have calmed down.

The second thing that happened was the non-event. Or the giant sucking sound, as Ross Perot would say. The markets for consumer-grade and business-class PTT that everyone banked on disappeared.

And now it looks like some carriers, like U.S. Cellular, are taking their PTT offerings out of retail. U.S. Cellular said that customers it initially planned to target with PTT were well-served by family calling plans and other group minute deals.

The only major U.S. carrier that seems to have any success with PTT is, you guessed it, Sprint Nextel. And the only MVNO that has had any success with it is Boost Mobile.

So does this mean that, except for Sprint, the market for push-to-talk is dead? Or are there some hidden success stories out there that I just don't know about?