i'm asking cuz i'm planing on buying one soon...
Sony Ericsson phones use their own OS. Currently, that is not an OS that is supported by Unity. The systems/OSes that are supported are: Wii, Windows, Mac, Andriod, and iPhone. Here is a link listing the different available Unity packages: https://store.unity3d.com/shop/
Thanks, Ares
Not sure about the "i" in x10i, but if that's the same as (or similar to) the X10, it is an Android based phone. If Unity will support anything less than version 2.2 (x10 if only version 1.6 for now), I do not know.