If the iPhone has OS 4 upwards, you can go into mail and view an inbox with all items, or individual mail accounts' inboxes.
To me, iPhone on ActiveSync (Exchange 2007) is OK for rough and ready users who literally want to check a message or send one.
It irritates me that I cannot mark things as read/undread, flag for follow up, or indeed any advanced feature at all. Read and send. And file. That's all I can do on iP3GS.
: Infrastructure Architect, Denver CO