Ok
I get an upgrade in two weeks and am tossing up between these two phones. iPhone 4 would be £67 per month and xperia play would be 59 per month on my tariff.
I have a ps3 so am tempted by xperia play, I currently have an iPhone 3GS. If I were to get a 4 I could sell my 3GS, if I got a play I would want to keep it for gaming/apps and music.
Does anyone have any opinions on which phone is better?

If your primary reason is gaming then you should take a look though the iPhone App Store and the Android Market and see which games they have that you want. Then check out the Sony Ericsson Play optimised games (there aren't many) and see what there is.

It's worth remembering that if you've bought a bunch of games on iOS, there's no way of transferring them to the Play. You'd have to buy them again on the Market.

Other than that, I'd say both the iPhone 4 and Play are good examples of a decent phone on each of their respective platforms. It's really whether you want a change and whether you've already invested a lot in one.