How to import Exchange Certificate into the android handphone?

This is setting up an MS Exchange Server 2010 with SP3 in a MS Windows 2008 r2-based AD Domain test environment. The mail is working, as setting up an MS Outlook (anywhere) on a laptop is working fine. Few of the client access roles, such as, RPC over Https, owa, EAS, autodiscover, are enabled. We are using MS Certificate service to be the Certificate Authority to issue Exchange Certificate for OWA, Outlook Anywhere, etc.

However, while try to setup the mail client on android phone using either Outlook or Exchange mode, both seem to have problem. Mail client may completed setting up, but attempt to sent email failed. A security error as follows is prompting:

     Security warning for usera@abc.com
 
     There are problems with the security certificate for this site.

     Certificate not from a trusted authority

     VIEW   CANCEL   CONTINUE

I can see quite a number of CAs located in the Trusted root CA store. My CA is in pcks#7 (.p7b), and the exchange certificate is in .cer format. I heard that this android ca store only accept CA in format of pcks#12 (.pfx), is that true? How can I proceed to import the CA into the trusted root ca store of my android phone?

Thanks,