Is your phone's bootloader unlocked? You can only flash custom kernels if your bootloader is unlocked. Not all of our phones are able to have the bootloader unlocked. There are threads in the forum to show you how to check if your phone is allowed to have it unlocked. If it says "No", then right now there is no chance of having your bootloader unlocked. If it says "Yes", then you can unlock it through Sony's dev website.
There are some great ROMs for the XPeria T that use the stock kernel. Right now, I am using XPerimenT ROM v2.9 on my LT30a. It's a little old, but I really like it. It is based the official 141 firmware.