Quoting from this press release:
AgileDelta, Inc., the leading provider of software for lightning-fast delivery of more content to more locations, today announced the release of its Axis 1.x and Axis2 Web Services Integration Kits for Efficient XML, the basis for the emerging web standard for binary XML. These simple plug-in integration kits allow the quick and easy addition of Efficient XML into any web service running on Apache’s Axis 1.x or Axis2 engine. The integration kits automatically detect and use Efficient XML for clients that support it and fall back to text XML for clients that do not.
Efficient XML enables applications and web services to encode and decode XML using a cross-platform binary XML format that makes XML data much more compact and transmits that data faster, using less bandwidth and battery life than standard XML. Efficient XML documents can be over 100 times smaller and faster than XML.
Note their performance and features page.
But Efficient XML looks poised to make a big impact, especially with smooth fallback mechanisms for supporting traditional clients.