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Most of the latest headsets are compatible with Xperia SP. I would recommend Skull Candy.
Have a look at this thread for a similar discussion http://talk.sonymobile.com/t5/Xperia-pro-Xperia-neo-V-Xperia/List-of-earphones-following-the-CTIA-st...
Follow the link below to have a better understanding of the standard http://www.xperiablog.net/2012/02/27/2012-xperia-range-uses-different-3-5mm-headset-standard/