My first guess was that this required a Google Apps subscription because of that. If I'm wrong, yeah, that could be a problem, but if you later change the produ

My first guess was that this required a Google Apps subscription because of that. If I'm wrong, yeah, that could be a problem, but if you later change the product to require a Gmail subscription, then you turn things around by becoming a value-add to Google's premium service, which I'd imagine they'd be quite happy about.