Can you use either the follow up flag to mark the items complete only if one of you has answered? Or how about categories? Can you create categories that represent the different states that the email is in, e.g., "I claim this as mine" or "This one is for you".

I think this technique (which I use with my tech support team) will depend on which smart phones you use and what they are capable of showing you about the email (i.e., do the phones show either the follow up or the categories).

Hope this helps!

Mike Sperry