FaceTime uses an active data connection this can be either wifi or your cellular data plan. Most carriers allow the use of FaceTime contact yours to find out.
For text messages this is little different. The messages app for iOS can handle both SMS and iMessages. SMS messages are the traditional text messages that carriers charge per message or have plans for (i.e. unlimited text). On the other hand iMessage is a data messaging service by Apple. It works on only Apple products (iphone/ipad/ipod touch/mac) and it uses an active data connection either wifi or your cellular data plan.
If you're iMessaging somebody it'll only use data and it wont cost anything but the data you're already paying for, same goes for FaceTime.