Howto convert MP3s into ringtones

You could simply transfer the entire MP3 to your phone, set it as your ringtone and be done with it. But most full-length songs are several minutes, and your phone only rings for about 20 seconds, which will mean a lot of wasted memory space for no good reason. Plus, you may want ONLY the Sweet Child o' Mine guitar solo halfway into the song to play as your tone, not the first twenty seconds of the track..