1. Follow Admin Guide to Add Device:
Go to Connections -> PSTN Connections -> Add PSTN Connection
2. Once you click on Add PSTN connection, Configure popup window by selecting Connection Type, then click next. Select Device Type as ISR2901. Continue configurate per the admin guide. Setting will vary based on your connection type and Service provider.
3. After completing the configuration for the new device(ISR2901), go to Devices you can see the newly added device and also Generate CLI link as well. Now use Generate CLI button to view CLI.