Q: The phone number "is not registered with iMessage"

yes, but first I had to do a number of actions.  Not sure if the order is correct, because I was just feeling around, trying to follow leads, and see what worked.

-open MMS in Messages under settings, so here Apple sent me a passcode which appeared on my computer screen, saying something new was going on, and did I approve

-then make sure the persons phone number was IN contacts, went to

-Messages/Accounts/Message Account/Settings - click add e-mail and enter the phone number.

-then in Messaage, open Preferences, Account and switch on  (somehow I had switched it to this 'Bonjour' thing.  who knows if that is what made a difference.

But voila! green name on messages, green, and message FINALLY delivered.

strange that it had worked for months and months, using my iphone5, but maybe stopped when I got the iphone6, and they did not tell me everything had to be closed and opened again.

Tried it, didn't work.  Got a pop-up on Messages on my iMac asking if I wanted to register a phone number with Messages, a number that previously was marked as not registered with Messages.  I clicked "Register with Messages" and nothing happened.  I still cannot use Messages on my iMac with that number.  Other numbers continue to work.  There are about 4 phone numbers that raise this issue, all numbers that previously worked.

But thanks for your help, appreciate it. 

that must be really frustrating - especially as the others work!  I tried to keep a track of all I did on an email draft, but maybe some was just intuitive and/or luck.  This is what I saved, if it is any different:

You must register your phone number by signing into iMessage from your iPhone. If you are already signed into iMessage on the iPhone, sign out and sign back in on the iPhone.

If it still doesn't appear on the computer, sign out of iMessage there and sign back in. It should appear then.

Also, in order to send SMS messages from the computer, you must enable it on the iPhone. In iPhone settings, open iMessage. Select Text Message Forwarding. You must be on the same wi-fi network. Your computer or other device should show in the list. Just click on the device you want to enable.

Also enable SMS on the iPhone.

See the answer in context

2. Messages/Accounts/Message Account/Settings - click add e-mail and enter the phone number.

3. Open Messages, click Messages>Preferences, open your Apple ID account within, on Settings tab add phone number in "You can be reached for messages at:"

in response to blackdogaudio

yes, but first I had to do a number of actions.  Not sure if the order is correct, because I was just feeling around, trying to follow leads, and see what worked.

-open MMS in Messages under settings, so here Apple sent me a passcode which appeared on my computer screen, saying something new was going on, and did I approve

-then make sure the persons phone number was IN contacts, went to

-Messages/Accounts/Message Account/Settings - click add e-mail and enter the phone number.

-then in Message, open Preferences, Account and switch on  (somehow I had switched it to this 'Bonjour' thing.  who knows if that is what made a difference.

But voila! green name on messages, green, and message FINALLY delivered.

strange that it had worked for months and months, using my iphone5, but maybe stopped when I got the iphone6, and they did not tell me everything had to be closed and opened again.

Whatever! who knows, when one contact's phone did not relay messages properly it was dumbfounding, and I solved it.  My son was not impressed with my ingenuity, no doubt figured it was just the old one dumbly wandering around, but it seemed to me it took about 4 or 5 separate interactions, and Apple support was no help. Keep googling your problem.

At one point - probably the crux: a message popped up on the computer that someone was trying to use imessage from a new device, and gave me a code.

so you need your computer open at the same time that you are working these settings.  good luck.

This is what I think the problem is:

1. If you are sending messages to an iPhone or another person on iMessage, the process works

2. If you are sending a message to a gmail user or other Jabber compatible users, then the process works

3. Problem is when you have to send to an Android user. This is where it fails.

Cheers

So? that does not lead to anything new.

the idea is to SOLVE the problem, actually, which I did.

For my case, my computer can now communicate by message to this person's phone, whatever their type of item it is.

I figured this system out, and it now my solution works, while it did not before.  Have you a clue as to how to advise someone else how to solve it for their system? not just analyze it? say so!

yes, it is helpful to know what it is that went wrong, but it is more helpful to get it to work.

if you keep at it, I am sure you will get it.

There is absolutely no reason to berate anyone on this thread who is merely continuing the conversation by contributing information that might help our investigation into what might be wrong. In fact their information was useful to me. What I do see is you repeating over and over again that you "solved" this issue, as though you're waiting for someone to congratulate you or to give you some kind of prize. Unfortunately, your solution has not worked for me, in spite of my trying to follow your instructions, which are somewhat incomplete.

The only thing I have found to getting around this problem on my Mac is this:

1. Open up your contact book from your Mac

2. Click on the contact you want to message

3. In their contact card, click on the type of phone number it is you want to message (i.e, work, mobile, etc)..right next to that number.  For some reason it won't highlight when you hover over the actual number, so hover over the phone number type.

4. It should highlight grey when you hover and pull up a list when you click that says: Call, Show in Large Type, or Send Message. 

5. Click on send message.  A dialogue box should pop up and you can type your initial message in there.  Once you have started the thread you can use the iMessage app to continue it.

Kind of a pita, but I couldn't figure out how to avoid getting the error message any other way with android numbers that were showing up as unregistered with iMessage.

sounds really good, thanks, I will try next android problem that presents itself.

After four hours of trying to troubleshoot this over a few days, you had the solution! Thank you very much! It is appreciated!

this might be as simple as one more botched update by Apple. For me, an  update signed me out of iMessages on the iMac. A simple check in preferences showed "signed out". At the same time an update on iPhone did the same thing. I have a feeling that they tried to beef up security and messed things up an unintended way. Every signing in to those "old" features prompts a security email that I have signed in with a new iMac, it is the same old one, or a new iPhone, which is still the same old one. Sorry Apple, I don't know who you are employing these days, or who makes decisions but this is not really top-notch, innovative anymore but reminds me at the worst Windows times, almost.

Regarding step 2: My drop down menu does not contain an item for deleting contact from the chat. It only shows phone numbers, New Email, and Contact Card. I am not using Yosemite.

Thanks.

Hi Glenn:

You said:

"If you are already signed into iMessage on the iPhone, sign out and sign back in on the iPhone.

If it still doesn't appear on the computer, sign out of iMessage there and sign back in. It should appear then.

Also, in order to send SMS messages from the computer, you must enable it on the iPhone. In iPhone settings, open iMessage. Select Text Message Forwarding. You must be on the same wi-fi network. Your computer or other device should show in the list. Just click on the device you want to enable.

Also enable SMS on the iPhone."

What do you mean by "sign out of iMsg and sign back in." I assume that means to go to Settings, select iMessage, and move the slider button from right to left and back to the right again so that the background area is green. If that is wrong please advise.

I followed your instructions to enable Text Msg. Forwarding. Only my iPad was on the list. I just realized that my Mac doesn't show up because it isn't connected to our WiFi network. It is hardwired via Ethernet for security purposes.

This problem of not being able to iMsg my husband's iPhone from my Mac has happened before. Sadly, I can't remember what I did to fix it! I have asked him to enable SMS in iMsg settings which he will do when he finishes his meeting. Hope this works. Curious why it would.

Regards.

Finally got husband's phone working with iMessage, but not sure how it happened. I had him check that "send as SMS" was on. It was. Then I had him toggle the iMessage slider button. Then I had him send me an iMsg, which I received on my iPhone in a gray bubble. Then I sent him a test iMsg which appeared in a blue bubble. Voila! Angry unsent messages on iMac iMessages were suddenly sent and appeared on my screen in beautiful blue bubbles.

Go figure.

Have a nice day.

I cannot text from my computer and I did everything that was suggested.  However, when I turn on the computer from my iPhone i recieve a message that a code was sent to the computer and I need to enter the code. However no code is showing up anywhere on my computer?? Any suggestions?

I cannot text from my computer and I did everything that was suggested.  However, when I turn on the computer from my iPhone i recieve a message that a code was sent to the computer and I need to enter the code. However no code is showing up anywhere on my computer?? Any suggestions?