If a bill is rendered to persons using intrastate telephone services or VoIP service, the amount on which the surcharge with respect to such services shall be based shall be the sum of all charges for such services included in the bill; except that if the person who renders the bill groups individual items for purposes of rendering the bill and computing the surcharge, then the amount on which the surcharge with respect to each such group shall be based shall be the sum of all items within that group, and the surcharge on the remaining items not included in any such group shall be based on the charge for each item separately.