how do i confirm if my number is registered with imessage?

On an iPhone, iPad or iPod touch go to Settings ➜ Messages and make sure iMessage is turned on.

Then go into Send & Receive, and make sure your Apple ID is logged in there.

On a Mac open the Messages menu ➜ Settings ➜ @ iMessage, and verify if your Apple ID is logged in there.

If you don't have a device to verify with then enter the number at Deregister and Turn Off iMessage - Apple Support

and click join Send code. If you don't get the code, and the website returns an error, then it's not registered with iMessage.

There are multiple ways you can engage with iMessage - AppleID, phone number, email address, etc.

Users can send a message to any of these and Apple will navigate the message to your iMessage inbox.

To check what methods are enabled, on either a Mac or iPhone, go to System Preferences (Mac) or Settings (iOS) -> AppleID -> Name, Phone Numbers, Email.

Here you will see a list of all the numbers and email addresses associated with your account.