How to map ProxyAddresses from AD to SharePoint?

I would like to map the ProxyAddresses field from AD to SharePoint.  I know this field contains information in AD.  It is supposedly mapped to 'SIP Address' by default but nothing is stored in that field.  I tried mapping ProxyAddresses to a new multiline field as well without much luck.  Any ideas?

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James Grizzle
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http://www.linkedin.com/in/jamesgrizzle