I modified your calc filed to this,
IF ATTR([Americas Category Subordinate]) = "Telecommunication" THEN [Variation Excl FX_Thousands] END
Because "Variation Excl..." is a calc field that is already aggregated, you don't need to SUM it again here.
ATTR wrapped around "Americas..." returns only single value "Telecommunications" for the aggregation.
Hope this helps,
EDIT: Looks like Deepak already answered it, my explanation adds to it.