4. FaceTime or iMessage are stuck trying to activate
One of the strangest (yet surprisingly common) error messages on FaceTime reads: "Could not sign in. Please check your network connection and try again." Similarly, if you check under Settings > Messages you might see a "Waiting for activation..." notice.
To repair these issues on iOS:
Visit Settings > FaceTime and tap your Apple ID.
Tap Change Location and ensure the correct country is activated.
Follow the same procedure under Settings > Messages > Send & Receive.
Make sure you are logged in to the respective services with the correct password.
Then, reset your device by holding the home and power buttons down simultaneously.
If this doesn't fix the issue, you might need to change your device's DNS settings. Try entering the settings for Google's public DNS servers, which could resolve your issue:
Under Settings > Wi-Fi, tap the name of your network.
Tap DNS and enter "220.127.116.11, 18.104.22.168" (without quotes).
5. Multiple iOS devices/Macs ring simultaneously when receiving calls
If you're among the Mac faithful and you get an incoming voice call, you might jump when your iPhone, iPad, and MacBook all begin to ring at the same time. This is thanks to an OS X Yosemite/iOS 8 feature called Handoff, which works as a call-forwarding system (among many other things). If you don't like your Mac ringing when your phone is at arm's length, here's an easy fix on your iPhone. Just visit Settings > FaceTime and switch "iPhone Cellular Calls" to off.
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