Currently Being ModeratedFeb 5, 2013 4:16 PM (in response to quentin DEWEZ)
Part of the imessage activation involves sending of a hidden SMS to a server which I believe is in London. If you are not in the UK and your carrier plan does not provide for sending of international SMS messages then that could be the problem.
Currently Being ModeratedFeb 6, 2013 1:02 PM (in response to Ocean20)
It comes from the fact that I had to make a moficitation for 4G LTE... so I cannot link my imessage with my phone number.
So I removed this modification and I'm back with 3G and imessage.