In the UK, the Xperia X10 has been released on T-Mobile. It’s available for free on a £35 a month contract, with the contract lasting 24 months. You can order the handset from T-Mobile but, they note it can take up to 10 days for it to be delivered.
Orange will also be stocking the handset but, they list the X10 as coming soon. Both Orange and T-Mobile will be offering the black version of the handset. While if you’re after the white model, it will be an Orange exclusive. There’s no information on tariff pricing for Orange but, it’s very likely to be the same.