I'd like to be able to tell to which network any mobile number currently belongs. Is this information available anywhere?

There are services that show the original mobile operator, but having moved my number several times, I don't even see the information for that.

No its not available. What telephone network someone chooses to use is their business no one elses.

As you point out you are able to find out the network the number was originally allocated to.

Eg : http://www.telecom-tariffs.co.uk/codelook.htm

What network they choose is their business of course, but it is not a secret and would be useful information if it was public.

One use of such information would be to know what are you going to be charged if you dial this or that number, many people have deals like free calls to the same mobile network, so the info would be useful in that case.

Hello!

If you want to know what telephone / mobile number is owned by then use this website:

http://www.numberingplans.com/

This is used by Police and other government bodies.

Hope this helps.

But that just shows "Original network provider" and specifically says "Number portability has not been taken into account," which was the point bigjohn made. It doesn't help with this particular query.