D-Link DCS-930L :: Use Of IPad And IPhone In 3G Mode

I just setup 3 webcam DSC-930L for a friends with a router DI-655.

I run the setup for the 3 webcams. If I use my dlink on the local network it work, if I used my dlink from let say at work, it work too. If I used the i pad in WiFi it works.

The problem is when I try to use the i phone or the i pad in 3G mode, sometimes it work but most of the time it doesn't, after about 60sec it says something like check your network settings... When I'm able to see something in my dlink app on the i phone, if I return back to the list after that it doesn't work if I switch camera.

Question is, do I have to forward any port on the router in the virtual server section? I'm assuming no since sometime it work and sometimes no. Do I have to activate the UpnP on the router too?