I rang O2 for my PAC code and asked if they are doing pre-orders, and was told categorically "no we wont, it will be first come first served on the 24th".
this coupled with the fact that Orange, 3 and Vodafone all have said they will be offering a pre-order service, i just found it slightly odd that the original carrier is seemingly the exception to the rule.
Just because an advisor tells you something (they really will tell you anything, even when they know nothing!), doesn't mean it's true. The advisors usually find out the same time everyone else does.
O2 will be doing pre orders. 100%. Mark my word!