There are corporate or enterprise versions of Windows XP that don't need to be activated quite the same way. Can you imagine a company with a few thousand machines having to indiviudally activate each machine? Didn't think so, and neither did Microsoft. Companies will quite often have one code that can be used on all of their PC's. There are corporate versions of MS Office that work this way as well.
The phone activation isn't that big of a problem in North America though as there is a toll free number you can call. I had to do this separately for both WinXP Pro and Office 2003 as I had re-installed too many times. Doesn't sound like this works as well else where though.
goates