I have a Nokia N95 and I've never been able to find a way to synchronise the calendar. I suspect the poet is right - he usually is - and that there simply is no way to accomplish this.
If your Nokia's can be synced online with Google, you could do it that way. I know they offer setup instructions, but can not test them myself. Here's what turned up when I looked;
If the setup instructions aren't for your model, try going to m.google.com in your phone browser. It should auto detect the phone type and offer whatever is available. http://www.google.com/mobile/more/
Then set up your google account on the iPad as an Exchange account like this;