I think that the professionally held belief that stammering can't be cured is probably correct. However, some techniques can give a level of control that has several outcomes. 1. The level of control gained can make it appear that the person doesn't typically stammer. 2. The stammerer can say any words they could have previously avoided almost always. 3. The stammerer doesn't usually feel anxiety associated with the fear of stammering before a speaking event. Now, lots of people would agree that this defines a stammer: control the things above, and you have cured a stammer. I have used words like "appear" "almost", and "usually" intentionally because the stammer is controlled, but it's still there. Maybe like an asthmatic who uses an inhaler - they still have asthma but it doesn't affect them routinely, but it can occasionally flare up. In the UK and worldwide costal breathing has helped thousands of people achieve the above. I have been using it for over 20 years - I can say what I want, when and how I want without fear, but I still have a stammer. I use a charity in the UK called Empowering Voices, there are other organisations you could use, but Empowering Voices is the only charity in the UK that teaches this technique.