[Note/Update: now that Apple has finally linked all the iMessage backend in iCloud you don’t need to jump through these hoops anymore. Just do this instead.]
Finally figured out how to make iMessage on my MacBook cooperate with a group text thread that includes non-iphone or Android users. This assumes that you have an iCloud account and you have an iPhone and want to send text messages to people who are not apple people. This solution allows you to send iMessages from your mac desktop to individual Android users or hybrid groups that include non-Apple users.
- Make sure you are logged into the same iCloud account on your Mac (go to System Preferences->iCloud) and on your iPhone (Settings, click your username at the top of the Settings list and go to iCloud). You likely are logged in as the same user but just sanity check this.
- on your iPhone go to Settings->Messages and select “Text Message Forwarding”
- Select your mac desktop from the list. Once you do, your iMessage application on your Mac desktop will display a string of numbers that you need to type into your iPhone to link up your iPhone and your iMessage app on your desktop.
Once I completed these steps I was able to send txt and iMessage messages from my desktop.