Citrix released an iPhone app - Receiver - that will put any Citrix XenApp hosted application on the iPhone. I had a client that ran ArchiCAD on a Citrix thin-client set up for a while and so it seems to me taht you could in fact run ArchiCAD on an iPhone.
Why you would want to is another matter.
discussion here: http://www.theiphoneblog.com/2008/11/15/citrix-brings-windows-iphone/
app here: http://ax.itunes.apple.com/WebObjects/MZStore.woa/wa/browserRedirect?url=itms%253A%252F%252Fax.itune...
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