The idea is that you become a confident speaker no matter you stammer more or less, which helps you become desensitize in regard to your stammering.
The technique is very simple:
At the beginning of your conversation on the phone or face to face, confidently say "I have a stammer, please could you bear with me". Then 99.99% the other person says "Yes, sure". Then you will have time to continue.
- Remember that this must be the first sentence of your conversation, afterwards you introduce yourself and say other sentences such as "My name is ...I am calling in regard to...
- Know that this is your absolute right to stammer and there is no shame on this.
- The other person understands that he/she needs to be patient while you talk and 99.99% of the situations people are nice and understandable.
- Besides, instead of feeling stressed and anxious you will feel confident and acceptable and you will have enough time to say what you want to say.
Here is another link to explain how to use telephone for people who stammer.
If you stammer sometimes like me, discipline yourself to practice this technique, desensitize yourself and boost your confidence.