Assume that Plan A has recurring fee $15.00 allows 10 widgets, with each widget over that costing $5.00, and Plan B has recurring fee $30.00 and allows 20 widgets, each widget over that costing $3.00.

My question is: If customer A begins on Plan A on Oct 15th, uses 14 widgets before the end of their billing period, and then switches to Plan B before the end of their billing period, are they just simply charged as if they had been on plan B the whole month (no overage for the 4 additions beyond Plan A (i.e. the plan they were on when the widgets were initially used)), or do they still get charged the overage from plan A, and plan B's recurring fee?

The hopefully simple answer I'm expecting is that the customer is just billed on whatever plan they are on at the end of the billing period, including the calculated overage charges, such that customer A that used 14 widgets and switched to Plan B before the end of the billing period would just pay the $30.00 for Plan B and no overages.