[fjtorres]

1- Kindles don't support mobipocket.com and mobipocke.com does not sell kndle content.
2- mobipocket.com content is sold to be used with standalone copies of the mobireader app, each instalation of which generates it own pid. You supply that pid so the content can be encrypted to that reader app. The app is free and prominently featured at mobipocket.com.
3- expecting amazon.com to provide user support to mobipocket.com customers is akin to expecting an Opel dealer to provide service to a Corvette. The two companies may be parts of the same multinational but do not share personnel, equipment, functions, or mission.
4- if you knew enough to find out how to calculate a pid for a kindle, which is an unsupported hack and might be illegal in some locations, the same sources could have told you how to get the file readable on a kindle. It is not a particularly hard process but the same legality issues attach.
5- as a rule, kindle carries a superset of mobipocket content. Buying it direct from the kindle would've been a lot easier. Or were you trying to circumvent georestictions or local taxes as well as the mobipocket DRM?

All in all, I think the amazon personnel just set a new high in politeness and bending over backwards in the name of "customer" service.