Once a user variable has been defined (see Managing User Variables), you can then use the user variables within any call flow actions.
Within a call flow a Set User Variable action can be used to set or change the value of a user variable. This includes using the current value of a call variable to set as the new value for the user variable.
Call flows can also be branched using a Test User Variable action to check the current value of the variable against a required value.
The existing value of a user variable can also be obtained using the variable $REG[name] in call flows. This allows a user variable to be used in the same way as a call variable. For example, in a Test Variable action.