asterisk users - Aug 2007 - Mitel IP 5020 phones

Hi, folks:

I've come into some Mitel 5020 IP phones. A client has made a
significant investment in them and we want to see if we can use them in
a new system.

Are these even SIP sets? I haven't been able to find out. Mitel's site
barely covers them (I was only able to find some user guides, which are
effectively useless; they say nothing about configuration and provisioning).

Has anybody used these with Asterisk? Any other feedback or advice out
there?

-Stephen-