At the same time, new 3G services will introduce much greater complexity in pre-pay. Because data charges may vary independently of time, it is not possible to predict at the start of a download the time at which a customer's credit will expire. Even if this were possible, it is by no means clear whether the service provider would want to cut the customer off mid-download.
Tax is also more difficult to handle in a multi-service environment.
Voucher schemes for topping up a pre-paid balance usually apply tax at the point of sale. However, if the pre-paid balance can be spent on multiple services with different tax rates, this approach can no longer work. At the time of sale, it is not possible to predict how much money will be spent on each service, and therefore how much tax will be due.