So far, I have received no official confirmation of this from IBM. As seen in their FCC filing, IBM have made a design decision to prevent certain cards from working. In conversation with IBM support staff, I have so far been told the following:
"The Mini PCI specification defines an alternate implementation for small form factor PCI cards referred to in this specification as a Mini PCI card. This specification uses a qualified subset of the same signal protocol, electrical definitions, and configuration definitions as the Conventional PCI Specification. Where this specification does not explicitly define PCI characteristics, the Conventional PCI specification governs."
Mini PCI is standardised by the same group that standardise PCI. Devices that conform to the Mini PCI specification should work with each other.
After speaking with a specialist I can confirm that only IBM wireless cards willwork on an X40 machine.
This prevents the customer to insert non-IBM cards that could adversely damage the machine and have it fixed at IBM costs.
This is the first confirmation I've had from IBM that the list exists. The excuse is, however, not obviously true. There is no restriction on inserting possible faulty devices into any other expansion slot.