Best App yet for the iPhone (for me and my circumstances, at least)...HeyTell. It's FREE, too.
It turns your phone into, essentially, a walkie talkie

It reminds me of the days I had Nextel Direct Connect phone some 9-10 years ago now.
A WAY cool app. You can even email your HeyTell messages if the other side hasn't received it thru the HeyTell system. I haven't texted since I got it, frankly - no need with voice communication/notes.
John