Or consider routing the call over 1899 from your virgin line. 1p per minute to ROI landlines, all the time. Calls to ROI mobiles 15p per min all the time.
http://1899.com/mobilerates.php
Or use 18185
Calls to ROI landlines 2p per minute
Calls to ROI mobiles 11p per minute
http://18185.co.uk/mobilerates.php
You can register with both carriers to get the best rates. You just dial a freephone access code from your virgin line, wait for the call to be answered then dial the full ROI number you require. Calls & charges listed through your online account within minutes of completing a call.