In case if you already have TF SMS numbers (US and Canada) and want to add a new one to the list, please do raise a ticket with support. We will be able to add the number to your account. 

Note: numbers are subject to availability.

Please note that you will have to either share the reference TF number which already has an approved use-case or if it is for the new/different use-case then please share the details as mentioned in this document. This will then follow the process mentioned here