Sure, So long as the device has a data connection then yes..
Could you double check the settings. I.e. Settings, Mibile, scroll down to hopefully see FaceTime and insure it's turned on.
Yes you can use facetime providing you have reasonable phone reception. Have a look at this link:
Edit: Sorry for the duplicate post, you got there first @caaf
Lots of Daves in this post.
I'm sure there is an echo, an echo
Still all good advice makes it worth while