I have a private VPN on my Iphone and Ipad, which I use for added security when, e.g. accessing my bank in a Wifi area. Is it necessary to use it when on the 3G or 4G system?

Richard

Even when on WiFi, so long as it's SSL enabled (every North American bank) connection you should be safe since the encryption is between your browser and the bank web server. Middlemen attacks would not succeed.

Of course VPN would act as an additional layer of security.

On Edge/3G/4G targeted attack on you or any specific individual becomes incredibly hard. Besides, they (that is bad guys) also have to overcome carrier's security measures to begin with.

I'd say unless you have a particular reason to be worried about a certain WiFi hotspot, SSL should be good enough.