The Register on "spinners": "Essentially what a spinner does is buy a new pre-paid handset and then burn up the inclusive minutes (talk time) which come with the accompanying SIM card. Once those minutes expire, the spinner throws away the new SIM and goes back to his or her old SIM (and accompanying telephone number)."
It's just hacking of the commercial models that phone companies put in place, isn't it? And not much differently from the folks who buy a phone "just for emergencies" - they're not generating revenue as a normal customer would, yet they benefit from subsidies and continual access to the mobile network, even if they're not using it. Of course, many of these customers succumb to temptation and become more conventional subscribers (which is perhaps why the operators let this happen)... but they're still gaming the system.
In fact in its early days, text messaging was another example of customers finding something their phone could do - but wasn't designed for - and putting it to good use.
As handset penetration hits and exceeds 100% (at least here in the UK), we'll see more of this. For instance, customers might buy a PAYG handset for incoming calls to keep their number consistent and avoid paying monthly charges, and keep another handset (with constantly "spun" SIMs) for outgoing calls.
I remember when I were a lad there were similar tricks for pay-phones - some would allow you to dial a number and get about half-a-second of conversation before the machine realised you hadn't deposited any money and cut you off. Just enough time to say who you are and request a call back from a friend or parent, say.