To set up an iPhone to access VPOP3's mail, you first of all need to configure VPOP3 to allow access by remote users (unless you will only be using the iPhone in the office, connected via WiFi to the office LAN).
These instructions apply to the iPhone, iPad and iPod Touch, and are for iOS5. Other versions of iOS should be similar On the iPhone:
For general advice on using mobile devices, see Using a mobile phone with VPOP3
There are two methods to support SSL encryption in email. The current way uses the same 'port' as normal, and sends a command to start encryption, and an obsolete way uses an alternate port.
It appears that the automatic setup system for iOS mail accounts only handles the obsolete method, even though the mail client itself handles the current method as well.
So, to use SSL encryption, follow the steps below (yes, it is a bit dumb that this is necessary (other email clients handle this automatically), but talk to Apple about that):