The first successful MVNO in the US came only 3 years after the first successful MVNO in the UK and mobile number portability was put into law in 2003 for both the US and the UK. The additional benefit is that because mobile numbers and wired numbers share the same area code base in the US, US number portability is basically universal. I don't see the basis based upon your listed criteria for saying that the FCC cares any less or that Ofcom cares any more about promoting competition.

Slightly unrelated but I find the idea of a mobile phone sharing an area code with landlines utterly bewildering. A phone, that by definition has no fixed abode, is now tied to a location and subject to long distance charges based on that location (As it was explained to me in Canada at least).

In a time when mobile phones were scarce, putting them on a local area code ensures that a large portion of their usage (calling to and from landlines within a geographic space that actually IS limited) doesn't require additional long distance charges for everyone. These days it may seem like a quirk, but really what 20-year-old technology decision doesn't?