Interesting! I think in the past UK networks have always been reluctant at allowing freephone calls at free/cheap rates as they have always feared people undercutting their own voice services by using calling cards etc. However, these can hardly be too much of a threat anymore, and besides some networks like Giffgaff already offer free 0800 calls. I have noticed that calls to freephone numbers are already free from other mobiles in many parts of Europe. (e.g. Spain)
I presume this change will imply that the owner of the freephone line will have to pay a much higher per minute incoming charge for calls that originate on a mobile network, when compared to those that come from landlines. Several owners and businesses might even just block calls originating from mobiles. This is the case in Spain where as far as I am aware all freephone numbers maybe technically free from mobiles, but several do not actually work. That's hardly a user friendly solution anyhow.
Same in many countries - callthough numbers either blocked or the provider charges higher tariffs to their customer to cover the cost they are paying the network
I had to ask someone in Germany to test about 8 or 10 freephone numbers in Germany before I found one that worked, and that had a 9 pence a minute surcharge. 13 pence a minute to call UK was ok for me at the time, until it became possible to call for 8 or 6 cents a minute using new mvno brands.
A few years ago, some joker launched a callthrough service with one or two pence a minute calls from freephone numbers. Or so he said. I was sceptical, and asked if he was sure about that from for example a KPN callbox at Amsterdam airport, which I said was impossible and KPN would certainly either charge or block, based on comments I'd read elsewhere. I got into a discussion with Martin Lewis about this, and he reckoned I was being too critical, and he'd given the bloke permission to reply to service queries. 3 weeks later a thread on MSE had whinges from someone who'd spent all their credit calling UK from a Tenerife callbox, at an apparent tariff about 6 or 10 times that published. 3 weeks after that the website went offline ...
So, taking that waffle partly into account, overall I reckon if Ofcom manages to thrash out an agreement on this, it's reasonably likely we aren't going to be pleased with the results as far as callthrough use goes