Here's an out-of-order list of techniques we discussed:
Count to ten in your mind. Take a deep breath.There's nothing wrong with getting mad,
Cut off the conversation. Resume later if necessary.
On the telephone, cutting off the conversaton may even give you the chance to "get in the last word" with someone who isn't letting you talk.
Learn and practice relaxation techniques, until you get good at them. Eventually they will do some good. Release your bodily tension and see if you can visit your internal "happy place".
Plan your conversation. Know your anger-triggers, and anticipate when they will be pushed. This helps to establish a sense of control. A lot of people hate feeling out of control in these situations.
As much as possible, understand why these triggers anger you.
Accept your personal limitations and triggers. People often are extra-frustrated because they are angry at themselves as well, wishing they could be more cool-headed.
When NOT in the situation, as a fantasy exercise, imagine letting loose on the object of your anger. This may help if part of your discomfort is horror at your own aggressive feelings.
Avoid situations that trigger your anger.
Before the fact, beware of over-rehearsing for upcoming confrontations.
After the fact, beware of over-replaying the confrontation.
but losing all semblance of reason is bad.