I say "Hej" as my informal Esperanto hello.

Remember that y doesn't exist in Esperanto, so "Heyo" is a non-starter.

I have never heard "ahoj hoj", that must just be a Freenode thing.

I do answer my phone with "ha lo" if I know it's an esperantist. I can't remember if I've heard other people do it though.

If it's me calling them, and they answer however they answer, I respond with "Saluton, parolas Erinja"

slu, as mentioned, is used by exactly one lernu user who isn't an experienced speaker. I wouldn't use it.