>I have a .net dll (not mine - a 3rd party) that I registered using regasm /codebase that returned 'Types Registered Successfully.' I can successfully call class methods in the dll from C#. To do so, it is along the lines of:
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When you register a .NET dll with /codebase, you're basically registering any of the exposed COM classes - so the various DECLAREs you've tried won't work (since that's not the correct way to call a COM component). I'd suggest opening the object explorer and looking through it to see if you find the PowerPhone* COM assembly. This is assuming they even have COM-accessible interfaces defined in the .NET assembly (if there isn't then you're not going to be able to do that either).