Making extra cash from "special numbers" [Brit]

I got an automated SMS from O2 today. It says:

From 28th Sept calls starting with certain numbers e.g 0844&0845 will be charged outside your incl. mins & cost 20p/min. Details at o2.co.uk/specialnumbers.

I figured that on the site there would be information explaining why this is the case. I pay £50 a month on contract and get a bundle including 1,000 free texts and 250 free minutes which means that every month I pretty much guarantee I only have £50 to pay.

The one 0845 number I use regularly is that of my bank, First Direct and occasionally the likes of BT or a utility supplier. Up until now, these calls which (the bank notwithstanding) inevitably resulted in me sitting listening to hold music for a good few minutes have been free. Now I'm going to be paying for them, and o2 have just slapped this new charge on me with no explaination why.

Am I wrong to feel put out by this? The soul-less o2 website reveals nothing at all, just a slightly more verbose equivalent of the SMS I got. Its all rather bollocks eh?

I'm going to write a letter to these people and send it COD. Two can play at this game.