From the iPad SDK, it looks like the iPad can make emergency calls.
The above was easily achieved by enabling a passcode lock, and then entering it incorrectly about 5 times. You can then slide for a emergency call.
We’re not sure why Apple included this functionality, but it may be related to FCC regulations that all wireless “phones” be able to make emergency calls, even if the phones aren’t currently active or even assigned a number.
If the iPad can make emergency calls, it likely has the ability to make normal calls, though we’d seriously doubt that Apple wants calling to be part of the iPad experience (or compete with the iPhone). Hopefully Apple will let Vonage, Skype and other VoIP applications on the iPad, however.