Yes and no. You can only make Wi-Fi calls on an iPad when paired with a T-Mobile iPhone. To do this you need an iPhone 5c or later running iOS 8.0 or later. Here's how to enable Wi-Fi calling on an iPad (or iPod touch):
1. Enable Wi-Fi calling on your iPhone by navigating to Settings > Phone > Wi-Fi Calling.
2. Tap the "Wi-Fi Calling on This iPhone" slider so it is ON / GREEN.
3. On your iPad sign in to iCloud and FaceTime using the same Apple ID you use on your iPhone.
4. Open your Settings app and navigate to FaceTime > Calls from iPhone.
5. 4. Tap "Upgrade to Wi-Fi Calling".
5. Enter the six-digit code on your iPhone and tap "Allow".
Now you will be able to make Wi-Fi calls on your iPad.