Wait, why did people stop checking email? I don't see how that relates to the open plan office. I've worked in open-plan offices and team rooms before, and people were generally pretty responsive on email and IM.
Like I said, it can backfire in weird ways. I think it happened because the silence rule made people stop verbal communications, which is the most natural thing in an open office, and it never switched to using email because well...it seems weird to email somebody who's right there. So email clients stayed closed and the communications culture just generally shut down.
Odd. Everywhere I've been with an open office, it's perfectly normal to use electronic chat with someone who's next to you. I guess you would want to make that part of the culture early on, to make it less awkward.