Ive been meaning to change my mobile number for a few months now (felt like a change, had the old number for over 2 years, too many people have it), so I finally did it today.
And I have to say I am impressed. Phoned o2 customer services (answered in less then a minute), asked if I could change my number, the woman said of course, found me a new number and told me to turn my phone off.
She activated the new number and advised me usually it changes in less then two hours, but the standard time is upto 24 hours (I remember the last time I changed, it took 4 days lol).
She said to just turn the phone on every hour or so to test it.
Anyway, I turned the phone back on after I finished the phonecall to customer services and got the error "Sim Card Not Valid".
So I left it for about five minutes longer and hay presto I turned it on and its changed without problems!
I was expecting to have to wait a few days or summit, but its all done already, its even updated on my online account which is surprising as usually anything takes upto 40 hour to be shown on that.
So well done to o2!