By releasing software from the iPhone 3g and 2.0, iPhone has emails, contacts, and calendars stored on the organization's mail server. This article outlines the steps you need to have access to your inbox from your iPhone.
Exchange Server 2003 with Service Pack 2 or Exchange 2007
A digital certificate in the Exchange environment is installed
Runs firmware for iPhone 2.0 or higher  Exchange Server Environment
The ActiveSync protocol used to communicate between the iPhone and the Exchange server must be enabled and configured on the server. The server requires a digital certificate to ensure communication with the iPhone. If you are using an ISA server, you must configure it to enable ActiveSync traffic in the Exchange environment. The fastest way to verify that the server is properly configured is using an ActiveSync test tool that identifies configuration issues.
Setting Up the Firewall
The Exchange Server and the network are protected from the Internet by using a firewall that needs to be set up for iPhone to connect to the Exchange via the Internet. To do this, you must enable the Internet on port 443 (port used for SSL) on the firewall and configure the firewall to transfer any traffic from the Internet to port 443 in the Exchange environment.
On the iPhone, select Microsoft Exchange from the Mail Services list. The next screen on your iPhone asks for your email address, username, and password. This username and password are the same as signing in to your office computer. The iPhone will try to automatically discover the server and probably fail and ask for the server name. Enter the Internet name of the firewall (eg Firewall.example.com) and not the name of the Exchange server for the server name. On the next screen, you can choose what to synchronize (email, calendar, and contacts) and how many days to keep the emails stored on the iPhone. When you've finished setting this up, touch the sync button to retrieve your mailbox.
If you are in trouble
A wide range of technical issues can prevent successful iPhone linking. To avoid technical complexes, consider using a hosted service for iPhone integration. Using a hosted feature eliminates issues with certificates and firewall opening and makes it easier for non-technicians to integrate the iPhone Exchange.