EE AFAIK have made available all the Xperia 1 series handsets on contract from launch date.
Ominously the Xperia 1 vi website doesn't mention EE on tne pre order option. So sadly this maybe an O2 exclusive.
EE may have dropped Sony for a number of reasons such as low demand, poor perceived value, difficulties in obtaining satisfactory servicing and perhaps reunaway demand for its nearest Android rival the Samsung S24 Ultra. When picking a handset for their contact customers, EE have to be as near certain as possible it will be a success with low returns, high spend per handset and something that presents a real alternative to the Samsung/ Apple near monopoly .Maybe on this occasion they might have decided not to proceed with the VI.
It might also be down to the backers of O2 dangled a huge order in front of Sony in return for an exclusive.
Whatever the case I think the decision for EE to pass on tbe Sony Xperia 1vi has been taken and a reversal is very unlikely.
