Enrique has been using Sprint's Push to Talk feature from the US to Mexico, but it's being discontinued and he needs an alternative. Sprint will be replacing Nextel PTT with a version using LTE, but that's still just on the horizon.
Leo suggests looking for an app that will take it's place on a smartphone. There's an app called Zello (iOS). It's also available on Android, Blackberry, and even PC. Enrique may even wind up liking it more.