With the iOS 8 Continuity features you can make and receive phone calls on your iPad or Mac using your iPhone, provided they're all on the same WiFi network and using the same iCloud account.
However, my wife and I both use the same iCloud account and we both have an iPhone. It's the same iCloud account that's configured on the iPad (and on my Mac). In the settings for FaceTime both on iPad and on the Mac, under the heading iPhone Cellular Calls it says These calls will use the caller ID +xxx xxx xxx xxx, and the number is my wife's cell phone number, not mine.
In the situation I'm in (2 iPhones using the same iCloud account in the same house), how can I tell FaceTime which iPhone it should use for the continuity calling feature?
Apart from the caller ID issue, I can't make calls from my iPad or Mac using my iPhone (when my wife's phone is out of the house). It says "iPhone Not Available. Your iPhone and Mac must be on the same Wi-Fi network". However, if I receive a call on my iPhone it appears fine on both iPad and Mac.