how do I keep the time of my ...

I travel all over the world and almost always put appointments first into my iPhone, since I rarely am at home. The iCal on my iPhone is therefore my principle diary and that on my Mac Pro effectively the backup. When syncing with iTunes (I think) the time of the entry I originally made is changed during the sync by the difference in time between the time zone I was in when I entered the appointment, and my home time. This makes my diary useless, and some of the changes I have made to repeat items have completely scrambled themselves.
When I put an appointment in my calendar for 11.30am that is what I want. I do not want my phone, or home computer, changing it to 12.30 because I was in Germany when I actually got the email organising the meeting and recorder the appointment in my diary.
To be honest I would have thought this would be the default, since I do not know anybody who would intuitively think that keying in appointment times offset by the difference in time between their current zone and where they will be in the future.
Perhaps the programmer does not travel much.
I have seen a "floating" time zone choice in the support pages, but can not find how to set it on my iPhone. I have updated to v3 iPhone, my Mac Pro is 10.5.7
Anybody knows how to relieve this frustration?

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