My iPad won't receive texts

BernardRosie wrote:

It's almost as if the number asso[s]ciated with my iPad sim card doesn't exist.

That is exactly correct!

Your iPad is not a cellular telephone. SIM card or not, it has absolutely no ability to send or receive SMS or MMS messages. It may send or receive iMessages, or it may use your iPhone in a Handoff mode to send or receive messages that way.

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. If you have added a DataSIM and Cellular plan to a WiFi+Cellular model of iPad, the number associated with the SIM card is only used to identify your account for billing purposes. This number is not used for making calls or sending messages.

However, when paired with an iPhone, the capabilities of iPad 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 (green bubbles) 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

BernardRosie wrote:

I find it odd they offer the option of a sim card for the ipad if it has no ability to use it.

You can certainly use it. It provides the ability to access cellular data. If, for example, you were at a beach with your iPad and no iPhone (if you had an iPhone, it could provide a Hotspot to access data), you could access the internet using the SIM.

SMS and MMS messages do not use cellular data. They use the voice frequencies, which are not accessible on an iPad.