Apple added the ability to make and answer calls on your iPad with the release of iOS 8.0, but your tablet needs to be connected to the same Wi-Fi network as your iPhone for this to to work. Here's how to set up the Continuity feature for all your Apple devices:
1. Sign in to your iCloud device on all your devices running iOS 8.0 or later. Your Mac needs to be running OS X Yosemite.
2. Make sure all your devices are connected to the same Wi-Fi network.
3. Sign in to Facetime using the same iCloud account.
4. On your iPhone navigate to Settings > Phone an disable Wi-Fi Calling if it is enabled.
To make a call on your iPad tap or click any phone number in Contacts, Calendar, or Safari.
You can disable this feature on your iPad or iPod touch by navigating to Settings > FaceTime and turn off iPhone Cellular Calls
Users who want to make free calls from their iPad without an iPhone can use the Facebook Messenger app to call their Facebook friends. Your iPad needs to be connected to Wi-Fi for the call to be truly free, otherwise standard data charges apply.