iPhone iMessage on multiple iPhone with same phone number not working

Hey,

I've been reading the MacRumors forums for years, now it's my first post here, so hello everyone!

I've got a problem:
I am using iMessage with my iPhone 5s and my Macs. I mainly use my phone number for iMessage. I got an iPhone 6 Plus, which I want to use in addition to the 5s. Both devices share the same phone number, but do have their own SIM-Cards (at least in Germany this is called "Multi-SIM"). When I added the 6+ to my lineup there were no problems, all iMessages sent and received showed up on all devices. Everything was perfectly synced.

I then changed my iCloud password, what I do every now and then. This is when the problems started. I had to sign in on all devices again and activate iMessage. On all non-iPhone devices (iPad and Macs) everything was fine. But on my iPhones everytime I activated one device, the other was automatically signed off from iMessage, i.e. it only syncs the messages that are sent through my e-mail iMessage accounts. Then the message popped up whichs asks me to activate iMessage (if I click ok, a background sms will be sent to activate the phone). This specific phone is then again activated for iMessage but the other one does not sync the iMessages sent to my phone number and asks me again to activate iMessage.

What can I do to use iMessage (with my phone number) on both iPhones? As I've said, it worked well until I changes my iCloud password.

I've contacted AppleCare but they couldn't help me. That was kind of a bummer.

Thanks in advance!
Henning

 

Do you mean in settings.app? Sure, but the phone number is only active on one device. On the other one the number is grayed out. If I deactivate and reactive iMessage on that iPhone, the number isn't grayed out anymore but iMessage is inactive for the first iPhone.