Sure. All you need is WIFI access.  Basically the non 3G iPad is an iPad on steroids. So if you could get your ipod touch to do a VoIP call, then you can do it on your iPad… And there are plenty of Apps to choose from.

Line2 has the most professional options. (My Review of Line2) I like that you have a dedicated number with mailbox, redirect, quite times, and can support calling in as well.  HOWEVER, the app has to be running for you to get an incoming call. I think that will be sorted once jailbreak is in place and we can run that app in the background.

There are plenty of other options; Skype, TruPhone; Fring, Google Voice (requires jailbreak)  I have a list posts on VoIP here, so you can read and choose the best app for you.

You may also want to invest in a good wire or bluetooth headset. Holding that big iPad to your head is optimal and it makes you look plain silly. 🙂