It looks like Windows Marketplace for Mobile is due for an update later this month that will allow users to switch regions. It’s possible that this new version of Marketplace for Mobile may include other bug fixes, plus some sort of integration with Windows Mobile 7 or 6.5.3. Over at the MSDN forums, a Microsoft employee said the following in response to a question about the Windows Marketplace for Mobile:
At the moment, it is not possible to purchase an application which is submitted and showcased on the US Marketplace if the purchaser is not in US. It is applicable uniformly for every marketplace.
We apologize for any inconvenience that this may have caused to you.
Microsoft is working on it and the facility to purchase applications from any of the marketplaces, while not being present in that particular country, will be made available later this month.
Thanks for the tip, Jose!