Welcome to Apple Support Communities.
It's my understanding that you're unable to activate iMessage on your iPhone 7 Plus. I do have a suggestion that may help with this. Check out this article and try some of these steps: If you get an error when trying to activate iMessage or FaceTime
The last step would be to contact Apple Support if you're still unable to get iMessage to activate.
If you get an error when trying to activate iMessage or FaceTime
To use iMessage or FaceTime, you need to activate them on your iPhone, iPad, or iPod touch. If you see an error message during activation, follow these steps.
When activating iMessage or FaceTime, you might see one of these messages:
- Waiting for activation
- Activation unsuccessful
- An error occurred during activation
- Could not sign in, please check your network connection
Check your device settings
- Make sure that you’re connected to a cellular data or Wi-Fi network. If you're using an iPhone, you need SMS messaging to activate your phone number with iMessage and FaceTime. Depending on your carrier, you might be charged for this SMS.
- Go to Settings > General > Date & Time and make sure that your time zone is set correctly.
Turn off and restart iMessage and FaceTime
- Go to Settings > Messages and turn off iMessage.
- Go to Settings > FaceTime and turn off FaceTime.
- Restart your device.
- Turn iMessage and FaceTime back on.
Still not activated after a day?
It might take up to 24 hours to activate iMessage and FaceTime. If the issue continues after 24 hours, follow these steps:
Let me know if this helps.
Thank you for using Apple Support Communities.