It was one of the huge apple iphone "advantages" when launched and they insisted that all the providers who wanted an exclusive launch with iphone supported it.Originally Posted by Wendy, post: 283211
So, O2 had to buy servers and stuff to support it and put them on their network.
After that period of exclusivity ran out (2 yrs after the first iphone) the other networks could then sell the phone and werent subject to the same requirements. They looked at the cost of providing the service and decided that plain old voicemail was good enough
As a consequence, in the UK, O2 pay monthly iphone tariff is the only way for ukers to get official apple iphone visual voicemail.