When making changes to users or user plans mid month, a charge and/or credit "Adjustment" will appear on your next monthly recurring invoice.  User changes include additions, deletions or changes from one user type (or calling plan) to another.  The prorated monthly fee (shown as "Adjustment" on your invoice) will either be a new charge when new users are added or a credit when users are removed. These charges will be calculated based upon the days the service was rendered during the month.