iPad iMessage or FaceTime on wifi without phone number?

Can an iPad on WiFi be used for iMessage or FaceTime, if it is not associated to a cellular phone?

For example, if my mom does not have a phone, but I buy her an iPad mini and get her set up with an Apple ID, can she use iMessage or FaceTime via WiFi?

I'm not interested in other WiFi apps like WhatsApp or Skype. It has to be not-complicated, and usually iMessage and FaceTime "just work" (the whole premise of Apple products).

Technically she does has a basic flip phone. If I buy my mom an iPad, I'm sure I can't associate the phone number for the basic phone to the iPad.