These instructions are for configuring a new Calendar account on iOS for iPhone, iPad and iPod Touch. The version of iOS used for these instructions is iOS v6.0, but they will probably work or help with other versions of iOS.
You need VPOP3 v6.0 or later for this to work. Note that a known issue in VPOP3 v6.3 may cause authentication problems - this should be fixed in VPOP3 v6.4.
If you now go to the Calendars app in iOS, you should see the VPOP3 calendars listed when you press the Calendars button.