Virgin seem determined to maintain confusion on this issue, as they still boldly advertise...
"Make unlimited calls to Virgin Mobile phones from your Virgin home phone
Got Virgin home phone? Any calls you make to Virgin Mobile phones from your landline phone will be free of charge, so you can easily stay in touch.
Your unlimited calls only last 60 minutes at a time. If they last longer than that you may be charged. But don’t worry… Simply hang up and redial before the hour’s up and you can continue chatting for free!
AVAILABLE TO VIRGIN HOME PHONE CUSTOMERS ONLY"
It says nothing about exceptions, disclaimers etc so can reasonably be taken at face value, & that's why so many people are unsure.