The iPhone ships with integrated Exchange ActiveSync, allowing it to interact with an Exchange environment much like any other smart phone based around ActiveSync. This technology provides users with push email and calendar support as well as access to an environment's global address list. The iPhone also supports Exchange policies of passcodes required to unlock the device. Finally, it offers remote wipe capability using either the Exchange administration tools or Outlook Web Access.
In many ways, Exchange management for an iPhone is similar to managing other smart phones that support Active Sync using either the Exchange ActiveSync Mobile Administration Web Tool (Exchange 2003 or 2007) or the Exchange Management Console (Exchange 2007). This only makes sense, as Apple licensed the ActiveSync software from Microsoft so that the iPhone could access an Exchange environment without requiring any additional server components. That said, not every Exchange environment has experienced a seamless pairing with the iPhone. Apple's iPhone in the Enterprise discussion forums have a lengthy series of threads describing problems uncovered by early iPhone-adopting organizations.
In several cases, problems seem related to a variety of Exchange configuration variables. Because Exchange deployments can vary widely, the exact nature of some of these issues can be difficult to provide with broad troubleshooting advice. However, a number of issues seem to relate to security options that rely on digital certificates to ensure secure communication. In particular, self-signed certificates (those created and maintained within an organization without the services of a certificate authority) seem to create problems. Overall, it looks like a large number of issues are configuration-related and resolvable, though at present it may take someone very familiar with deploying and managing Exchange (and/or a fair amount of testing) to resolve issues in some environments.
Also important to note is the system requirements for Exchange support of the iPhone. An Exchange 2003 environment must be running Service Pack 2, and an Exchange 2007 environment requires Service Pack 1. Earlier Exchange versions won't function properly (if at all) when an iPhone user attempts to configure and access his or her account.
Even in a perfectly functioning Exchange environment, the iPhone's Exchange support has some limitations. Several Exchange features are not implemented, including folder management, accessing links to SharePoint servers, task sync, creating an out-of-office auto-reply, creating meeting invitations, or flagging messages for follow-up. Another point to consider is that when Exchange is used, users can't sync contacts and calendar data with their computer via iTunes (much as consumers cannot sync via both iTunes and Apple's MobileMe service).
If your business doesn't rely on Exchange for email and collaborative tools, you still can implement the iPhone using any IMAP/POP mail server. The major drawbacks are that you won't be able to implement over-the-air calendar and contact sync options, and users will have to rely on fetch-based email (where the iPhone checks email automatically at intervals of 15, 30, 45, or 60 minutes, or in response to a user manually checking for new mail). If you're using a non-Exchange mail server, users won't be able to sync calendar or contact data over the air. In these cases, sync via iTunes will be the only way for users to sync such data with either iCal and Address Book (Mac OS X) or Outlook (Windows).
You can implement IMAP/POP email for an internal email server or an account hosted by an Internet provider. One option worth exploring if you want to implement the features available from an Exchange server is hosted Exchange services. These are companies that provide full access to an Exchange environment, complete with collaborative tools, push email, and other features, for a monthly fee. For smaller businesses (and even some larger ones), this approach provides all the benefits of an Exchange environment while allowing you to offload the actual configuration and maintenance of that environment. Some of this functionality is delivered by Apple's MobileMe service, but MobileMe isn't really designed for interaction between multiple users in a business environment, and likely will be adequate only for very small businesses.
Following are some hosted Exchange providers to consider:
Given some of the problems noted earlier, before you sign up with a service you should verify that the provider has tested its services with the iPhone.