Email & Calendar?
These seem like basic functionalities of a Smart Phone that Google would undoubtedly include by default, and/or a least offer, via application download in the Android Market. I can't imagine you would have any issues here.
Contacts & Push?
Anybody's guess here. The amazing thing about Android is that its open source so, if something doesn't exist that is already being done on other phones, chances are Android could support it. Will a developer take the initiative to develop it? Who knows. This is really wait and see
The Bottom Line
If you were a consumer I would say go ahead and get an Android device because with the possibilities inherent in Android, all these things that you want/need are bound to pop up if they don't exist from the getgo.
But, since you're a consulting firm considering adopting android for business reasons, I would dissuade you from being an "early adopter". I'm the biggest Android enthusiast there is, but from a business standpoint, I wouldn't want to risk making the switch to an unproven platform that you know virtually nothing about in a real world setting. The result from investing money into a system that ends of being buggy and WORSE than your original will not make very many people happy.
There will be plenty more Android Phone's coming out in early 2009. I would recommend following the launch of the HTC Dream closely and pay attention to the Android Market and Android Applications and see how people are reviewing them in regards to Enterprise Solutions.
Come early 2009 when you have a new budget and solid reviews and information about Android in a business setting you'll have a lot more hardware AND software to choose from.
I know my answers were vague, and there isn't much of a way around it. That's why I think you should inherently take a "wait and see" approach for your business.
Hope this helps