You have to give it to the guys at XDA-Developers, they really do some great work. Shortly after Android 2.1 was released for the Nordic market, the guys worked out that you could change your X10i to be Nordic branded and thus update to Android 2.1. Unfortunately this was only for X10i owners, as owners of X10a handsets have different base bands and therefore, if the Nordic branding worked, 3G would no longer be available.
With still no word from Sony Ericsson on where will be next though, this has caused quite a bit of uproar and many X10a owners disappointed. Fortunately Bin4ry at XDA has been hard at work. It is now possible to flash 2.1 to an X10a handset and 3G is confirmed to still work after wards. You just need to turn off your phone, run the X10Flash bat file and follow the instructions. It only currently works on the Xperia X10 and not the X10 Mini, Mini Pro or X8.