Yes, you can make an outbound call to the SIP URI of a Plivo application. For example, you can make an HTTP POST request to originate an outbound call to "sip:example@app.plivo.com," which is the SIP URL used to identify the Plivo application.
If you’re expecting to receive calls to your SIP URI, you must create an SIP endpoint that's attached to your Plivo application in the Endpoint tab. Share this endpoint with others, not the SIP URL of your application.