For email, I've started using VistoMobile. This will sync your lotus notes inbox with your iphone using an IMAP configuration. It requires a desktop client and only available on windows.
VistoMobile provides a web lookup to the corporate directory. This is limited to email, at this point, and only allows an email to be created with a single address.
For Calendar entries, I setup a forwarding rule in Notes to forward meeting requests, updates, etc. to a Live Mail account. Using the httpmail plug-in for Leopard, I can access these on the MAC to update ical, even from behind the corporate firewall.
Entries that I add on the iPhone, I forward to the corporate account once they are sync'd with iCal. Not ideal, but it works ok for me while I wait for a single complete solution.