An iPad, whether a Cellular model or not, is not capable of directly accessing Cellular Voice or Messaging features. An iPad with Cellular connectivity alone can only access IP-data services. An iPad is not, and can never be, a standalone substitute for an iPhone.
However, when coupled with an iPhone, the capabilities of iPad significantly broaden to include access to Cellular Voice and Messaging services of the associated iPhone - relayed to the iPad over WiFi using Apple’s Continuity features. For the most part, an iPad using Continuity is able to access Cellular calling features, of the iPhone, when both the iPad an iPhone are in close physical proximity and are connected to the same WiFi network - but this is not the end of the story.
Now, if your both your Cellular Carrier and your calling plan support WiFi Calling, your iPad can make and receive calls independently of the iPhone - even when the iPhone is switched off, elsewhere, or using a different WiFi network. Not all carriers support full WiFi calling.
The settings that you need to change/verify on your iPhone and iPad are:
On your iPhone
Settings > Mobile Data >WiFi Calling >
- WiFi Calling on This iPhone - set to ON
- Add WiFi Calling for Other Devices - set to ON
Settings > Mobile Data > Calls on Other Devices >
- Allow Calls on Other Devices - set to ON
- [Allow Calls On] - explicitly enable your new iPad from the list of devices.
On your iPad
Settings > FaceTime > Calls from iPhone > Calls from iPhone - set to ON
Additional information about Continuity and the relevant Cellular services can be found here:
Continuity
Work across all of your devices seamlessly – Apple Support
SMS/MMS Messaging
Forward SMS/MMS text messages from your iPhone to your Mac or iPad - Apple Support
WiFi Calling
Make a call with Wi-Fi Calling – Apple Support
Making and receiving calls on iPad
Make and receive phone calls on iPad - Apple Support
When correctly configured, the iPad FaceTime App provides access to Cellular Voice Calling features - whilst Messages supports SMS/MMS messaging services.
In conclusion, in conjunction with an iPhone, it is theoretically possible to configure WiFi Calling service for your iPad. After WiFi Calling is enabled and configured, your iPad can make and receive cellular calls whilst connected to a WiFi network (caveat: any associated firewall must not block WiFi Calling or VoIP services) - even in absence of the iPhone.
