I’m wondering on how to get a phone number on a iPad

iPads are data only devices.

Even if you have a cellular iPad, it doesn’t connect to the voice channels.

The only way to receive/send sms messages or make phone calls is to have an iPhone using the same Apple ID.

See this:

Make and receive phone calls on iPad - Apple Support

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 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.

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

Carriers provide SIM card for iPad but for data only no with phone number , if you are using an iPhone and you are using the same Apple 🆔 from the iPhone in your iPad you can set up in iPad your iPhone phone number using wi-fi calling because in USA 🇺🇸 of others countries you can do phone calls with a iPad using your cellphone service and your iPhone could be off or on to do phone calls with the iPad , in USA 🇺🇸 with AT&T and others carriers they provide wi-fi calling in all data plans

Make calls using Wi-Fi on iPhone - Apple Support (CA)