ios 9.2.1 cannot accept imessage

Have no clue what you mean by rejected.

So here are some links for you.

Use Messages with your iPhone, iPad, or iPod touch - Apple Support

If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support

If you get an error when trying to activate iMessage or FaceTime - Apple Support

Thanks for the reply.

Rejected means "not shown in my mesage windows on IPhone".

It show up in my IPad 2 (still on ios 7) or IMac (on El Capitan) using the same ICloud account.

I have found all the tips link on your reply and did them all but it still does not work.

Any idea if Apple can revert back to older IOS?

You cannot revert to an older iOS. Apple does not support that.

Given that, it sounds as if your iPhone iMessage is not activated correctly. If you go to Send & Receive in Settings>Messages, do you see your phone number checked off? When you go into Settings>Messages, do you see any messages under iMessage?

If you go to Send & Receive in Settings>Messages, do you see your phone number checked off?

Yes, I checked all that.

Settings>Messages, do you see any messages under iMessage?

IMessage can be sent ...... (no special message or non activated IMessage).

IMessage is turned ON also.

All the IMessage if it shows up in the Message windows has become Green also as supposed to blue before.

This happened for new contacts, all the old contact pre-upgrade to 9.2.1 still show up as Blue.

I have also tried to change the type to "IPhone" in address book because I know they have IPhone.

Thanks.

Do you have cellular data turned on when connected to cellular, or if you are connected to Wi-Fi?

Is anything else checked off in Send & Receive on the iPhone? You need to have a valid data plan to send/receive iMessage. Besides a reset an a Network reset, what other troubleshooting have you tried? It appears that you have text message forwarding on, as well as continuity, since you are using an iPad and iMac to do messages. The next steps in user troubleshooting are restore from backup, and then if necessary restore to factory.

Everything is turned on.

It happens whether I am on cellular data or WiFi, does not matter.

It is AT&T service if that makes a difference.

I have been on 20GB Data plan with them.

Use probably less than 1GB so there is no data shortage.

The setup works when I had 9.2, exactly same setup and it started to act weird when upgrading to 9.2.1 last week.

Check everything online and do the turn off and on, airplane mode, go out of ICloud and go back in, change the ICloud password, Reset the network, reset the phone, restore the phone. Nothing fix the issue.

Wonder if Apple knows of the issue???