Why can't I send or receive text messages on a cellular ipad?

Do you have an iPhone - or just an iPad?

An iPad, whether a Cellular model or not, is not capable of directly accessing Cellular Voice or SMS/MMS Messaging features. An iPad with either WiFi or Cellular connectivity alone can only access IP-data services. An iPad is not, and can never be, a standalone substitute for an iPhone.

However, If paired 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.

More information about Continuity and the relevant Cellular services can be found here:

Continuity

Use Continuity to connect your Mac, iPhone, iPad, iPod touch and Apple Watch – Apple Support

SMS/MMS Messaging

How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support

WiFi Calling

Make a call with Wi-Fi Calling – Apple Support

If you have an iPhone - and both iPad and iPhone are signed-in to iCloud with the same AppleID, to send SMS/MMS messages from your iPad you must explicitly enable Text Message Forwarding for your iPad on your iPhone...

On your iPhone:

Settings > Messages > Text Message Forwarding - set to ON - and explicitly enable your iPad from the list of devices.

Also ensure that Messages in iCloud is enabled on both your iPhone and iPad:

Settings > [Your Name / AppleID] > Messages - set to ON

As for the NHS Covid Track & Trace App, it’s functionality is again tied to that of mobile phone - and is not compatible with iPad. Your phone sits in your pocket/purse and goes with you wherever you go, whereas an iPad will not be on your person at all times. The phone tracking functions and proximity to you are what make the App important.

As for being a “proper” cellular device, the cellular models of iPad are precisely that when cellular services are activated on the device. However, tablet computers (like iPad) can only access cellular IP-data services - not voice and legacy SMS/MMS services that are “cellular phone” services.

I hope this information, insight and clarification is helpful in improving your understanding of both cellular services - and the respective capabilities of iPad and mobile phones.

It is a cellular device. It is not a cellular telephone. SMS and MMS. Require a cellular telephone. Any data only cellular device is incapable of sending or receive SMS/MMS texts as those require a cellular telephone voice connection. Nowhere has Apple ever described an iPad as a cellular telephone device, and the very term “cellular device” has never been synonymous with “cell phone”. There are lots of cellular devices that connect to the internet over a cellular network providers service but that have no cellular telephone connection.

Any data only cellular device can use any one of many internet messaging services, and make and receive VOIP telephone calls.

Apple 2FA does not use SMS texts by default. The default way of receiving authentication codes is via an encrypted iCloud notification to your trusted devices. The codes are only sent by text or voice if you don’t have access to any of your trusted devices and specifically request a code to your backup cellular telephone number.

And putting your iPad SIM in your iPhone or any other cellular telephone won’t let you receive texts. The SIM in your iPad set up for cellular data services doesn’t have SMS enabled on the account. The phone number on an iPad does nothing for the iPad itself - it is used by the cellular service provider for their internal billing system. It is not a functional cellular telephone number.

The one, and the only way, for any iPad to receive cellular telephone SMS/MMS texts is by pairing the iPad with an iPhone to use iOS/iPadOS continuity to share the iPhone’s texts with the iPad.

Functionality has not been limited at all.

Your understanding and expectations of Cellular services clearly need some additional insight...

Cellular Telephony services include legacy SMS (Short Message Service) and MMS (Multimedia Messaging Service). IP Data Services are an additional/different technology - and offers different capabilities.

An iPhone and other modern Cellular telephones can access Cellular Voice and Messaging services - and IP Data services.

An iPad (and all other manufacturers tablet computer devices) can only access IP Data Services. Some Apps can add VoIP (Voice over IP) and proprietary messaging capabilities - but these all operate over IP Data.

To reiterate, a tablet computer is not a Cellular telephone.

No, it depends on what the account settings provisioned on the SIM are. When used in a data only device, carriers don’t enable things like SMS since the device cannot use that anyway. If your carrier allowed you to use an cell phone SIM with a fully active cellular telephone service account set up on it then it may still work in a phone. But then your also paying more for that data only service in the iPad than you may have to - there may well be ipad specific data plans available for less.

An additional feature of a Cellular iPad, not present in the WiFi Only models, is GPS.

GPS functionality is an element of the Cellular Chipset - this not being present in the WiFi Only models of iPad.

There are other differences between WiFi and WiFi+cellular iPads. Only WiFi+cellular iPads have aGPS systems (WiFi only iPads use things like WiFi location database information or Bluetooth micro beacons for location data). This is why WiFi+cellular iPads are popular with pilots, boaters, campers and so forth as they can have maps and location data available offline. It also, obviously, allows use of data connection when no WiFi is available but cellular is. My sisters cottage is far too remote to get any conventional internet service, so no WiFi. However, there is a cell tower in a nearby provincial park that provides signal, so they use a MiFi and a cellular data plan when there, and regular WiFi when back home where they have hi-speed fiber internet. So there are plenty of instances where having cellular data capability is desirable.