Delta allows upgrades both internationally from the US and domestically on "select fares", which currently are Y, B, and M. All of these are usually expensive. Domestically, one can upgrade from Y for fewer miles. Here's a link to the Delta award chart:
http://www.delta.com/skymiles/member...ards/index.jsp
AA is looking better and better these days...
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Time..... is on my side.