Hi, is there a way to represent both sequential and parallel tasks at once within one project?

i.e. "Call Joe", "Email Mary", then "deliver boxes".

I don't necessity need to "Call Joe" prior to "Emailing Mary", these aren't dependant tasks in my project, and I can do either as soon as I decide to enter that particular context. But, I do need to both "Call Joe" and "Email Mary" prior to "delivering the boxes".

I guess I'd like the ability to mark any number of disparate tasks in a project as "available" as opposed to all of them, or just the task at the top of the list being "available".

Is there a way to do this currently in OmniFocus?

Thanks!
Ethan