Facetime uses around 200-300 MB per hour. You would need around 600MB if your phone doesn’t download anything else. The only package to accommodate that is the 1Go/89$ one.
Your main problem would be reliability of the connection, both onboard and through the satellite link. There are dead spots onboard, so you would need to find a suitable space with a strong wifi signal and the appropriate environment.
The satellite link is unreliable at best. If you are in port, the CM’s use their down time to use it. Sometimes, the link is too slow to even do emails.
I would schedule the call on a port day and find a restaurant with a Wifi connection if you can.
