Any mobile device, like the ones being discussed in this thread, that has WiFi capability, can do VOIP calls and texting. 2G/3G/4G service is not needed for this, at all. A smartphone with no 2G/3G/4G service is not capable of making cell calls, but it can still be set up to make WiFi phone calls. It just needs the right apps installed to make it happen.
The GrooveIP app is the dialer app (if needed), Google Voice sets up the WiFi connection through a phone number. Google Talk can then be used as the texting app. All for free. As long as you have a WiFi connection, you're golden. And there's no "activation" involved with any carrier...you're using a WiFi internet connection...whether it's yours, or a public one.
P.S. There are other apps available to do these things. But I'm only familiar with the ones mentioned above.