In fact (especially for you lot saying data shouldn't expire) there should be no data bundles in existence and thus no rollover or expiry, and you should just get a fixed uncapped line speed. If you can't afford the high cost* of the 1mbps (or more) wireless, connection, you'll just have to be happy with your 256kbps speed
*just the fact of limited spectrum
Costs and limited spectrum are NO excuse for expiring "data" which does not exist anyway. There is no justification for the expiry of "data" plans other than in invalid business plans based on mostly fictitious scenarios, one of which was tabled in the article that triggered this discussion.
There are no differences between networks whether they are wireline ( copper or fibre) or wireless (FWA or mobile or satellite), when it comes to capacity constraints. Each network has its own specific constraints. when capacity runs out, any "new" connections must wait until some capacity is released by someone else.
The mobile industry has for years played the scarce spectrum card, sometimes justified and sometimes not. In this case, that card means absolutely nothing.
A customer chooses to (because the network providers allow for it), a postpaid or a pre-paid option.
The post-paid customer pays a fixed access charge (or should be paying such a charge), which gives him access to the network to use when he wants and for how long, which then gets charged for based on his usage.
The pre-paid customer goes to a provider and says in essence:
"here is xx Rand which I am prepared to pay you now so that I can use the network when I need to and for how long. I am of my own free will, giving you my money in advance".
Both want to be able to use the service they have paid for and neither should find their allocation is limited because they failed to use the facility it a fixed time period. It is just plain and simple theft.
Any spurious justification whether is it scare spectrum or otherwise, dos not make up for the fact that operators are stealing from their customers when they make data packages expire.
There is absolutely no correlation between the costs of building, maintaining and replacing the network and the expiry of packages whether they are for minutes, SMS's or data. It such dependencies exist in a business plan, then they exist because the business plan has artificially created such a dependence.
At the time when you try and use a network, it is congested, overloaded or busy, it does NOT matter in the least. You as the user have to wait regardless until some capacity is freed up.