I've been hunting down a good deal on the Sony Ericsson x10 since it's release, and this appeared on Phones 4u yesterday! By far the cheapest I've seen, and easily beats the X10 tmobile deal posted last week!
It's free from £25 a month on O2 with 300 minutes, unlimited text with a 24mth contract
Free from £35 a month on Vodafone with 900 minutes, unlimited texts and unlimited mobile internet on a 24 month deal!
I've personally gone for the vodafone offer for the internet!