There have been numerous reports about problem with FaceTime and iMessage. Some users got the message like “Waiting for Activation” or “An error occurred during activation”, and others seem to be getting a network error of some kind.
There have been
numerous reports about problem with FaceTime and iMessage. Some users got the message like “Waiting for Activation” or “An error occurred during
activation”, and others seem to be getting a network error of some kind.

Many users tried fixes some fixes like :

AIRPLANE MODE CHECK
SIGN-OFF AND THEN
SIGN-IN WITH YOUR APPLE ID
RESET OR RESTORE
HARD RESET
RESET NETWORK
CONNECTION
But all the fixes mentioned above didn’t worked. They got message like “Activation Unsuccessful” , and can’t send or
receive texts with iMessage nor can’t make a call with FaceTime. I think it’s Very frustrating!
Here’s the tutorial
how to fix iMessage and Facetime on iOS 8 

Successfully..

It’s really simple. All
you need to do is follow these simple steps:
Go to Settings
Scroll down and tap on
iMessage.
Tap iMessage white
button to green.
A pop up message box will appear.
There have been numerous reports about problem with FaceTime and iMessage. Some users got the message like “Waiting for Activation” or “An error occurred during activation”, and others seem to be getting a network error of some kind.
Now don’t tap on OK.
Just CANCEL it.
Wait for second, enter
your apple id and your iMessage is activated successfully.
You can now send
iMessage to any other iOS devices.
Likewise its same for
FaceTime too..
Tap FaceTime white
button to green.
It will pop-up a
notification
There have been numerous reports about problem with FaceTime and iMessage. Some users got the message like “Waiting for Activation” or “An error occurred during activation”, and others seem to be getting a network error of some kind.
Just CANCEL it. Wait
for a moment and enter your apple id.
You can now make a call
with FaceTime too.
Try this trick couple of times and it will definately work for you.
Let us know your opinion in the comments section.