I think it will come down to four things: Who buys the phone; whether IT thinks its secure enough; whether it will integrate well enough; and whether IT trusts and has relationships with the vendor (s).
The Phone Buyer
This is the one area that I think favors Apple initially. Right now employees actually make the decision to buy the phone and their company simply reimburses them for some or all of the charges.
Apples primary and overriding focus is on the buyer and cool technology that pulls those buyers in like bees to honey. Folks lust after iPhones and, at least for the moment, no other phone creates the unbridled lust that this device creates.
Recently I was on a panel at the Information Week 500 conference and the CIO that shared the panel with me indicated he would like to give all his employees iPhones and this was a Fortune 500 insurance company and Microsoft shop.
Unless the Google G1 phone can close this lust gap or change this one dynamic, the iPhone has a significant advantage here.
The iPhone has had a number of security problems and the G1 is mostly untested with regard to security.
Both these phones are likely to be viewed as relatively unsecure, though the G1 largely uses online resources. This suggests the security problem it probably has is largely mitigated because the phone doesnt actually contain much confidential information (if deployed properly).
The G1, deployed properly, is basically a terminal to enterprise applications through the browser and as long as proper access security is used it should be competitively secure. On the other hand the iPhone is not only a more traditional phone, it is connected to MobileMe which pulls enterprise mail into an Apple service which hasnt been working that well.
Even the idea of another company getting mail from an internal source, particularly an executive, is likely to make some security folks catatonic. MobileMe potentially requires, in a secure environment, a security audit, This is because its a repository for confidential information and if it isnt secure could provide sensitive information about anyone, both personal- and job-related, to the world.
This means that while there doesnt appear to be a differentiating advantage between the two devices both are relatively unsecured the MobileMe service would likely fail the iPhone in secure environments.
Apple simply doesnt play well with others and that is likely one of the reasons MobileMe isnt working out very well.
However to integrate into IT systems you have to be able to work closely and honorably with people you might otherwise view as competitors. Google is vastly better at this, given that their tools cross a wide variety of vendors who preload them on PCs today.
Because they have to generally run on Microsoft platforms they seem to know how to develop products that function there and have more than a passing familiarity with UNIX and Linux. While not as good at integrating as Microsoft currently is, they are vastly better than Apple is. That gives them the lead in this category as well.
Trust and Relationships
Googles failures with Gmail are well known and they are gaining a reputation as a vendor who sells thing of questionable quality.
Worse, they tend to do some incredibly foolish things with regard to EULAs, which effectively translate ownership of things that were written or created using a Google tool to Google. They have promised but not yet delivered anything approaching a solid cloud-based application offering. And the reliability of this phone solution isnt yet known but suspected to be buggy and unreliable.
Apple isnt much better. The latest iPhone has had a series of nasty problems and Apple has generally treated IT managers as if they were clueless idiots.
They dont think of IT as partners for anything and have a nasty habit of trying to cover up serious problems like security exposures. Trust doesnt run deep with Apple outside of Apple shops and this suggests that both companies, for the moment, are tied at equally bad.
I do think Google will resource this to fix it long before Apple even considers trying to work with IT again. So my expectation is that, while theyre currently tied, Google will eventually win here as well.
Wrapping Up: Who Wins
If we went by category Google would win by a landslide, but the first category the buyers themselves in most companies easily overrides almost all of the others combined.
This suggests that favoring Apple might have the better path if it werent for one thing: the Chrome browser.
This browser, as an application front end, will exist broadly on both G1 phones and PC desktops, allowing IT to more easily roll out cloud-based applications that will run on both platforms. If Google can create compelling devices, coupled with the fact that Google is agnostic about both carrier and cell phone manufacturer, will push Google ahead. They will emerge more dominant, much as Microsoft emerged more dominant after the first Mac vs. Windows wars.
For the enterprise it is all about scale. Both Google and Microsofts models scale better which, in the end (much like it impacted the Mac) are what makes for a winning combination. In the end, for the enterprise, I think we will have Google and Microsoft battling it out for the top position and that this will be a fight for the record books.
In closing, and on a related subject, if you are planning to get a G1 you might want to wait until late November or December and until we both know what the major bugs are and know that most have been corrected before getting one of these G1 phones. Generation One products tend to be a problematic and it generally is better to let someone else experience the initial pain.