If you want to see your Lotus Notes Calendar AND your own iCal calendar on the iCal application on the iPhone, there is a solution.
a) You must (or your company) have a server running Domino 8.5.X (preferably 8.5.2), also must have a software called Lotus Notes Traveller which as I understand makes it possible for putting the events on the iPhone, using the Active Sync tecnology from MS.
b) The way it works is that the Domino server is configured by your system administrator, and then from the iPhone you access your company's specific web address where you download a "script"(the iphone side of the Traveler software) install the script and that's it.
You can look at this page to have a general idea of the procedure (remember the specific address should be given to you by your Notes administrator)
http://www.its.monash.edu.au/staff/mobile/pda/iphone/traveler-setup.html
However I have not been able to put Lotus Notes Calendar on the iCal on my Mac.
Also I used to be able to see my iCal Calendar on the Lotus Notes client on the Mac, but no longer works since Apple made changes to the Mobile me version of iCal