From the change log for php4.0.5:
Added new object VARIANT() to encapsulate values for use with the COM and DOTNET module. Therefore it is now possible to pass values by reference, convert php values to extended variant types (currency, date, idispatch, iunknown, ...) and define the codepage that should be used for unicode - conversion.
That's my best guess, but I don't know how to implement it yet.