There is space for an operator to be innovative here
I'd be happy if I could use my inclusive minutes for 08x numbers like this:
080x & 084x numbers use 2 normal inclusive minute per minute
087x numbers use 3 normal inclusive minute per minute
Yes its a steep mark up, but I'd see it as a compromise - I'd rather use up my inclusive minutes faster than have to pay ~25p/min at all times, even with loads of inclusive minutes left at the end of the month.
If you disagree - don't down vote - reply below with a better suggestion!
I've even said to my provider that I would take out a package with more minutes if they did this kind of thing, buts its out of bundle usage (i.e. charges when you're out of inclusive mins/texts or charge-at-all-times 08x numbers) where they make their money now.
The reason 0800 numbers got blacklisted from mobiles is that people started buying calling cards to make calls cheaper while the 080x call from the mobile was free (certainly on Orange and what is now T-Mobile). Now that kind of thing is only partly worth doing with those cards that let you ring a normal 01/02/03 number to make cheap international calls.