You should tell the WB then, since every Buffy/Angel episode ever done was billed as a crossover.
I’m a fan of both Angel and Charmed, but I don’t see a crossover working. They’re a different flavor, if you will. Angel dark, sometimes funny. Charmed kind of funny, sometimes dark. Charmed would have been great crossed with the short-lived (a 2001 news-marathon victim) Dead Last. I don’t know what I’d cross Angel with…maybe The X-Files(which would work with Charmed too) or The Profiler.