You will need to have Exchange 2003 SP2, but if BB is working then this should be fine.
Basically to need to set up OWA, OMA will follow and then the iphone should be able to connect.
Recommendation is that you use a trusted SSL cert.. From somewhere like godaddy.com ($36). If you have a front end and back end server then you should let the phoen connect the frontend server. Or better have an ISA server publishing the fronedn server.
Apple have an enterprise deployment guide that should be useful to you:
http://www.apple.com/support/iphone/enterprise/
Also a very useful guide here...
http://blog.fosketts.net/2008/07/10/how-to-set-up-iphone-exchange-activesync/
The iPhone tends to be very easy to set up.. Hopefully this will get you going. Post back if you have any questions..!