Hi,
On Iphone 6 - IOS 8.2 - Location India.
Facing the same issue since I upgraded to 8.2, this is what I have done for troubleshooting so far:
a) Switched off imessage reset network settings and restarted and turned imessage back on - does not work
b) Followed all suggestions related to time zone / locations settings - does not work
c) Downgraded IOS to 8.1.3 but then it did not take my 8.2 backup - so could not work with that (so never tried it)
d) Read somewhere to retype my phone number in General -> Phone -> My Number - did not make imessage work
e) Checked if 3G plan is active - it is - so that is not the issue - activating over wifi is not working either
f) Changed sim cards - no luck
g) Changed passcode - not working
h) Finally restored my iphone - fresh download of 8.2 - not working still
i) Disabled Continuity from IOS devices and imac. (thanks Noblecat for this one)
j) Waited 24 hours and tried all this again - no change
Also noticed:
- I can log into my icloud ID and use imessage with the caller ID as my email ID but the phone number does not show up - a temporary fix for those of you who cant do without imessage and are ok with using the email ID as your caller ID
- My other apple iphone 5S after s also not working BUT it was never upgraded to ios 8.2 - makes me believe this is an imessage activation server issue and not an IOS 8.2 issue.
- I made a few other friends (whose imessage was working fine) turn off and turn on their imessage - it reactivated fine and is working - makes me believe the server issue is not universal but affecting a few of us
Finally:
There was a system downtime of 12-15 hours where iCloud services went down on the 12th / 13th of March - I suspect the iMessage activation issue is connected to that. Called Apple support - they made me go through the entire troubleshooting and finally said that they are getting a lot of these complaints and it seems to be a server issue from their side. The Apple system status page does not show any issue though https://www.apple.com/support/systemstatus/ so this is definitely a subset of users problem and not affecting everyone. So they asked me to hang in there and wait until they resolve the issue - have a case ID from them will follow up and post if something new comes up.
Quite infuriating and an unproductive waste of time trying to get this to work.