hi
like everyone else in this thread, i changed from 1 SIM to another SIM, and could not get iMessage to activate to the new SIM.
in my case, the new SIM number was being read correctly (and since I am using iPhone 5 there was no way to enter a different one anyway). but it would not actually add the new SIM number and always failed at activation.
the old SIM number was also always appearing (greyed) as the number associated with that apple id.
apple has a a Support Article that says to dissassociate a SIM number with an apple id, you need to force a change by changing the password for that apple id. i did that as well, but still that apple id would not be removed from association with that old SIM number.
since I travel on business so frequently, I cant wait days or weeks for changed SIM numbers to propogate throughout apple servers and mobile carriers.
since the basic root cause of the problem is that there is high "stickiness" of a mobile number to an associated apple id, a different solution could be to make sure that each SIM number you use is associated with a unique apple id for that country. each SIM number you have is associated with a different apple id. so when you change apple id you "should" be getting the number you have associated with it in the past.
has anyone tried this solution to the problem?
thanks