Besides loading a new rom & hacking your Samsung Tab to make calls, you do have a couple other options that will kind of allow you to make calls.

One is using Skype - unfortunately you can't make calls via 3g, but have to be connected to wi-fi to make an internet based call.

Click here to learn about Google Voice on the Samsung Tab - you can't make calls, but at least you can text message and get voicemail.