I've just checked the article and it says they have lost the exclusivity contract, hence why later in the article it says...
"O2 will continue to sell the handset in Britain"
Nothing will change for current O2 users, it's just now that you can get the iPhone with Orange as well now. It's not such a big deal for O2 now since there are other excellent smart phones out there to compete with the iPhone. It was something special a few years ago but times move on. In fact, Apple have hacked me off at charging £6.50 for the software update to my iPod touch, only to ask for it again less than a year later. Could you imagine Nokia or Samsung billing you for updates?