Sorry to appear pedantic but the costs are:-

After 1min           18866 costs 0870 costs 

7.91p

After 10 mins      18866 costs          0870 costs 

79.1p

After 20mins       18866 costs        0870  costs

£1.58

etc etc - with the ratio of costs rising towards nearly 16 times the cost.

Using a basic cost comparison, as you do,  is meaningless in a case where one function has a step.
Your calculation to explain the difference in cost of 0870 numbers would be exactly what the proponents of 0870 would want - just look at the first MINUTE!!  It's not so bad then!
When was the last time you phoned a NGN and were only in a queue for ONE minute??
Sorry, I cannot accept the validity of your calculation.

Completely agree, Dave, that is why I tried to put some actual costs down in a table to show the increasingly large differentials.
The 0870 operators will be able to continue their revenue gathering from us until more people realise the actual costs are not what they think.  The common expression is "But it says that 0870 numbers only charge the National rate ...",  and so consumers THINK it's as cheap to phone them!!  WRONG, as my small table showed - only when more of us realise this will there be a chance to stop it.

Hi Guys,
I think the strategy here is to make formal complaints to OFCOM re the link between 0870 National Rate when it was introduced to how the de-facto standard (that it was linked/setup to) of BT has now fallen. I have been involved in Telecoms for over 15 yrs and the national rate was merely an extn of the local rate and freefone type service. This is now been turned completely upside down... and BT were in charge of numbering then, not OFTEL.
Incidentally, the 'company' that uses 0870 gets about 2p per minute on the inbound call for calls in excess of 100,000 mins per month; There are variations on this of course but that is the rough 'Book Price'. Also one of the reasons a company uses 0870 is not merely the mercenary instinct to make money from their customers, it is about them saving money.... They need to stop us ringing them with complaints. In these call centres, incoming calls means call queuing, callers get annoyed, stats are awful and then 'company' needs bums on seats to answer calls and provide service. This in turn costs lots of dosh, so the answer is to try and control the call volume by using 0870. Of course it is self defeating as the people that genuinely have problems end up paying for the previlege which is not good.
There is one other aspect I know the 'company' would promote and that is, it is revenue that goes back into the system to stop other price rises; At the end of the day they will get their money one way or another.

OFCOM's first big decision so far has been 'fudged', we will see when they finally make an announcement on BTs anti competitive behaviour of bundling option 1 into line rental. It looks like Ofcom will alllow BT to trample all over the market and they will defer to the big corporates. Don't hold your breath for a relaxtation of 0870... at least it is far more resonable than 0871, now there is a real rip off!! National rate 24 hrs x 7. Most companies & people think it is the same as 0870, just an overflow number set.