You can access a virtual private network (VPN) on your iPhone. This enables you to securely access your company’s network behind a firewall — using an encrypted Internet connection that acts as a secure “tunnel” for data.
The 2.0 version of the iPhone software supports something called Cisco IPSec VPN, which apparently provides the kind of security network administrators want.
iPhone also supports VPN protocols known as L2TP (Layer 2 Tunneling Protocol) and PPTP (Point-to-Point Tunneling Protocol).
You can configure a VPN on the iPhone by tapping VPN under Network, tapping Add VPN Configuration, and then tapping one of the aforementioned protocols. Then, using configuration settings provided by your company, fill in the appropriate server information, account, password, encryption level (if appropriate), and so on. Better yet, lend your iPhone to the techies at the place you work and let them fill in the blanks on your behalf.
After you’ve configured your iPhone for VPN usage, you can turn that capability on or off by tapping (yep) the VPN On or Off switch inside Settings.