For Standard accounts, only one user can be associated at the moment. We are working on this as a future enhancement, so stay tuned! 

For Enterprise accounts, you can add additional users through TelePortal if you are the Administrator of the account. You can assign user roles such as:
 

• Administrator: allows the user to have full access to all features in TelePortal
• Finance: allows the user to view reports, manage payments and view invoices
• Developer: allows the user to view reports, manage API keys, access troubleshooting tools 
• Support: allows the user to view reports and access troubleshooting tools