When trying to call a number using Google Voice on an iPad, I get the following error:
Cannot Open Page
Safari cannot open the page because the address is invalid.
Is there any way to place a call through Google Voice while using an iPad?
It seems that that page is currently broken and only works on iPhones. It doesn't work on iPods or iPads. You should use one of Google's other interfaces for placing calls.
There are several options:
You could also use an app like GV Mobile +, which, even though it's for iPhone, works just fine on the iPad.