The question of whether to get one's own 08 number to give to companies divides the users of this site.
Some think it's OK to "get their own back" whereas others see it as don't agree with it as it allows providers of these numbers to profit.
I would expect that the amount of revenue derived would be small. There is the question of whether providers pay out revenue straight away or wait until a certain amount is accrued which would be a barrier to generating revenue for the site.
As 0871 numbers are now officially Premium Rate Service numbers, service providers must register with PhonepayPlus, so in practice I think 0844 numbers are likely to be more popular with individuals.
There's a number of threads on getting your own 08 number such as:
Getting One's Own 08xx Number. Also (perhaps a bit outdated now) are those listed on the
Hot Topics thread.