It's not possible. You could use Paul Berkowitz's "Export-Import Entourage"
script set to exchange information between the two, but that's not a
preferable workaround.
<
http://www.macscripter.net/scriptbuilders/?search=Export-Import+Ent>
A better idea would be to set up one main identity for your use and keep all
of your contact and calendar information in there. You can have more than
one e-mail account in an identity; just go to Tools -> Accounts and set up
additional ones.
You can move e-mail between identities by dragging folders to the Desktop to
save them as MBOX files, and then by switching identities and dragging them
into the Main identity.
