iPad Air lost separate text number after reset

iPads can send iMessages to other iMessage users. They can send them using WiFi or cellular if that's an option. On their own, they cannot (and never have been able to) send SMS/RCS messages. In order for them to do that, they need to be connected to an iPhone.

Forward text messages from your iPhone to other devices - Apple Support

The mobile number assigned to your iPad was assigned by your cellular carrier when you subscribed to cellular service on the iPad. However, it was for billing purposes only. It has never been possible to use that number for messasging of any kind. If you want cellular service for your iPad, you'll need to contact your carrier and arrange to pay them for that.

I don't think you're lying. I think you're misremembering. I worked at Verizon Wireless for twenty years, including when the first iPad with cellular was released.

LSpain89 wrote:

I can assure you I'm not misremembering. It was an entirely separate phone number from my actual cell phone number

Yes, it certainly was. It was a unique number used for billing purposes. iPads do not now nor have they ever had a cellular voice chip. SMS is sent using that chip.

and I never paid for cellular service.

In order to have a number on the iPad, you would have had to have paid for cellular service. Numbers are owned by the cellular companies. Only they can assign them. There is no other way to get one.

I absolutely had the capability to send text messages on it somehow and I thought it was so cool that it had the ability to do that. My boss still has that number saved as my second number. Looking into this on my own earlier I found a few other people also recall being able to send messages through a number that came with the iPad and weren't paying for cellular service nor had it connected with their carrier. For some reason no one else seems to remember this, so at this point I'm going to blame the Mandela effect.

Yes, I do believe you are the victim of the Mandela Effect. But I've no interest in arguing you out of your belief because it doesn't affect the way things work now.

What matters now is that if you want to be able to send SMS/RCS messages with an iPad, you need to connect it to your iPhone using the procedure in the article I linked to above. And, unless you pay for cellular service, you will only be able to use the iPad to send messages (or connect to the internet in any way) by using WiFi. Right now, the only way to have a mobile number on a cellular-capable iPad is to pay for cellular service through a carrier. And even then, you will not be able to use that number for messaging.