If you want to connect from your iPhone directly to a network drive, you will need to install an app from the iTunes store. Apple provides no utilities within the iPhone operating system (iOS) that will allow you to do this. There are dozens of iOS apps that will allow you to connect to an iPhone as a network drive from a computer. Approaching the problem from the opposite direction, in which you want to connect to a network drive from an iPhone, there are far fewer choices, but a free app named NetPortalLite does offer this functionality.
Download and install the NetPortalLite app to your iPhone. Either install it directly to your phone using the "App Store" app on your device or download it into iTunes and sync the app over to your phone.
Connect your iPhone directly to the Local Area Network (LAN) with your network drive via Wi-Fi. By default, an iPhone will prioritize Wi-Fi over 3G connectivity. Check the top of your iPhone's screen for the blue Wi-Fi concentric circles. You may need to open the Settings app and configure the network if you have never connected to it previously.
Gather the address, login and password information for your network shared drive. Most network drives will support the Server Message Block (SMB) protocol and this is what NetPortalLite will use. In a business environment, you may need to consult with your support or systems administration staff for this information.
Open the NetPortalLite app on your iPhone.
Tap the "Machines" icon at the bottom of the display, and then press the "+" button in the upper right corner.
Enter any name you would like to identify the network drive for the "Display Name."
Enter the computer name or IP address in the second field. This may be a numeric address with four blocks of digits separated by periods or a single host name (for example, "netshare"). If the drive is located by the Domain Name Service (DNS) name, enter the DNS Domain suffix (for example, stratospherix.com).
Press the "Edit..." button and enter your user name and password to connect to the shared network drive in the second set of fields. You can leave these blank if you do not require them, and the "On demand" option will prompt you every time you connect.
Press the "Save" button in the upper right corner, and attempt to connect to the network drive by tapping on the newly created item in your list of machines.
If the network drive is on a windows machine, you may need to preface the user name with the Windows name of the domain and then a backslash. For example, if the domain is "win" and your user name is "joe," enter "win\joe" as your user name.