I've been making use of the Orange access number provided by pre-dial.com for some time now in order to get 0845 calls within my X-net inclusive minutes.  Time calling landline/0845 numbers accrues credit points to the originating mobile number which can then be cashed in for a more expensive call such as an overseas one.  Points can be gained by using the access number for any landline/0845 call, so there's little to be lost except a few seconds of X-network time in routing a high proportion of calls via this service.  The ratio of points to minutes is obscure, but three points seem to accrue for each two minutes of call.

I now find that points can be  employed to call 0870 numbers - the ratio can only be estimated, but it seems that for every minute you spend on a landline or 0845 call, rather less than 30 seconds of 0870 time is awarded.

So, the holy grail at last - free 0870 calls?

And no, before you ask or try it, 0871 does not work.