Yes, make sure your web site is hosted on a FP enabled server - you can then
logon to the internet on your lap top or whatever, Open the site live in FP
2003 and make the changes - since you're working on the live site, the
changes saved are immediate, and it drops the step of having to upload the
changed pages.
As long as you have access to a phone line, you can dial in from whereever
(bear in mind, that whereever you might be might not have DSL or broadband,
and you'd need to rely on a slow dialup connection).
Even better, if your calendar allows updates to it through a web-based
interface, all you'd need to do is visit that page on the web, and make the
changes through a web-form kind of thing like a Content management system
although limited to updating the calendar.