You can only make mobile phone calls and send and receive SMS through an appropriate service gateway. Most cell phone network providers do not allow their customers to access their respective gateways except through their respective cell phone network.
There are however gateways from other providers that allow you to make calls and send and receive SMS over the internet (e. g. over a wireless connection to an access point connected to the internet).
You can only make mobile phone calls and send and receive SMS through an appropriate service gateway. Most cell phone network providers do not allow their customers to access their respective gateways except through their respective cell phone network.
There are however gateways from other providers that allow you to make calls and send and receive SMS over the internet (e. g. over a wireless connection to an access point connected to the internet).