New Zealand carrier, 2degrees Mobile, have released a commercial celebrating the fact that they allow data allowance rollover. This means that any unused data that a customer has bought and paid for, but hasn't used, it kept for a subsequent month. Plans that allow rollover data allowances have been in existence for a number of years now and whilst not all carriers use it, and not all customers use it, it is nevertheless a nice perk to have, especially if you routinely use a little under or over your allowance. For the months you use under your allowance, the surplus can be carried over to a month you've overused your allowance. Different carriers have rules governing the data allowance rollover plans, explaining how much data may be rolled over either in a data or monthly allowance and for how long it can be left active on the account waiting to be used. Typically, only one type of data (either international or domestic) can be rolled over from month by month. In the case of 2degrees' plans, customers on the Carryover Plans are able to use their data and rollover data allowance when roaming off the 2degrees network and with Vodafone.
2degrees Mobile's commercial, linked below, shows two cell 'phone users discussing what might happen to their unused mobile data. The two have a number of interesting theories. One suggestion is that the unused data is sold on to the black market, where shady individuals might offer it to punters from their cars. Another theory is that the data is archived and stored in a warehouse, where it is left to rot (or decompose). Another theory is that the data might be smuggled out of the country to be sold off at a foreign data auction. The final point that the advert makes is that the unused data is sold on to customers every month, which in the words of one of the characters, "sucks."
More and more carriers are offering data allowance rollover plans in an attempt to jostle for position with each other. It is unclear how many customers across the world and what proportion of their allowance use the rollover facility, but as the trend is seen as more useful than not, this is a good thing. As for 2degrees, since the business launched into the New Zealand market in 2009 it has increased competition between the various carriers and this is a good thing for customers.