Sms ringtones type of file i have to use Today i downloaded some .mp3 short files...But when i try to add them as SMS ringtones it tell me that "This is wrong type of file"

In what type should i download those files so i can be able to add them as Sms ringtones?

My device is a Xperia X8
Android ringtones, more often than not, come in Ogg Vorbis format (.ogg), so you'd be better off using that format.

(It's weird that your device doesn't support MP3, mine works great when I put them in /sdcard/media/ringtones. But then again, every device is different.)