wifi connection to cellular network?

The wifi connection is a steady connection, u can use it only within its range without any interruption. But when using cellular network the speed varies with the signal of the phone and it is also a bit expensive affair.

It's not possible without using VOIP.

Even is you use the facilities within Skype to make incoming and outgoing calls, you will still be using VOIP.

There are several Apps, such as Skype, that allow free calls to other instances of the same App, but they do not allow connection to the normal phone networks for free.

As an extension phone, you might be able to connect the tablet by Bluetooth rather than WiFi so that you can use the tablet as an alternative to the phone itself. Most smart phones support Bluetooth connections for headsets or in-car hands free systems, but this will depend on whether the tablet can adopt that role.

That's the best I can offer.

bluetooth won't have the range. thanks but no voip services for me.