Is it possible to hack facetime call?
FaceTime calls are encrypted sufficiently for most anyone's needs. FaceTime's encrypted stream acts underneath any other WiFi encryption that might also be present. If you feel that end-to-end data streams encrypted with unique keys for each recipient is safe, then I'd say have fun with FaceTime.

Someone with special skills, tools and time could probably crack it, but you probably don't have a high enough profile to be worth the time/effort.