When we are developing something, I mostly prefer to keep the options open for the user.
** But depending on the development challenges, we can do:
1 - Have an option in the account online as Default Sender that will be enforced for when sending from CRM or other integratable apps
2 - If no Default is selected, the Ready to Use Options can show in dropdown in SMS Sending window on CRM and the user on CRM can choose a sender.
Since some SMSes may require a cross communication between our end and the client/contact/lead