Add a number
Open Telephony → Numbers and click +

Telephony → Numbers - the + button opens the number pool
Select a number and click Save

Available Numbers - select one, then Save
Click Connect to → SIP Trunk

A new number starts Not Linked - Connect to → SIP Trunk
Outbound trunk
Created automatically - for calls you make from your Unpod number. The moment you choose Connect to → SIP Trunk, Unpod creates the outbound trunk and the number turns Linked. Outbound is complete at this point - there is nothing else to configure.
Outbound Trunk Details - ready as soon as you choose SIP Trunk
Inbound trunk
You configure this - for calls people make to your Unpod number. Until you add it, the number shows Inbound trunk is not configured yet and inbound calls have nowhere to go.Click Connect under Inbound Trunk Details

Inbound Trunk Details - Connect opens the trunk form
Fill in the trunk

Configure Trunk - the SIP URI is where Unpod sends incoming calls
Test, then click Create Trunk

Inbound trunk configured - Configure edits it, Unlink removes it