For a phone, what do you need besides email and calendar?
I can't imagine being useful to connect to corporate shares or stuff like that, so getting email is all that matters. If your company has Outlook Express, an app like Mail+ on the iPhone (and probably Android) can access your email & calendar without any help from IT (or any ability on their end to wipe your phone, which is a deal breaker as far as I'm concerned!)
It worked well for me when I've had cause to use it. Being able to access corporate IM would have been handy as well, but not a show stopper.
Is it really useful to be able to VPN in and access internal web pages? I've never had cause to want to do so, but YMMV.