The EU Law Blog has a great post explaining a recent ECJ judgment on the mobile phone roaming charges. The case concerned the legality of the regulation establishing the cap on roaming charges, and I'd recommend the article if you're interested or want to get a feel for how the ECJ decides such things.
Another interesting thing (though it's not very surprising) is the behaviour of Vodafone (and perhaps the others, but it's Vodafone that stuck in my mind). When the roaming charges legislation was passed and being announced on the news, it was noticable that Vodafone had quickly got advertising out pushing the idea that it was reducing roaming charges for its customers - as if it was an entirely voluntary decision for the good of its customers/the business. It's not surprising that Vodafone was a bit upset at loosing a nice stream of income, but the litigation proves how willingly it adopted the change.