How do I send text messages to non-iPhone owners using the iMessage app on a Mac or the Messages app on an iPad? TL;DR

I was on ATT for years and could text iPhone and Android users with the iMessage app on my Macs and the Messages app on my iPad. I switched to T-Mobile (and ported over the same phone number) and now I can no longer use iMessage or Messages to text Android users except on my iPhone itself. How can I send and receieve text messages with Android users once again?

Devices that I Own


iPhone 6 running iOS 8.4 on T-Mobile Pre Paid with a ported phone number from ATT
iPhone 5 running iOS 8.4, but no cell signal. Used as iPod.
iPad Air WiFi running iOS 8.4
MacBook Pro Late 2013 running Yosemite 10.10.4
MacBook Air Mid 2012 running Yosemite 10.10.4


The Longer Story

I was on AT&amp;T for years with multiple iPhones and I was able to use the iMessage app on my Mac laptops and the Messages app on my iPads to send text messages to people who used Android phones. Apple users received texts via the iMessage protocol and those messages showed up across all devices as blue. Android / non-iPhone users in general always used SMS/MMS and texts showed up as green across all devices. I could switch between devices and continue conversations with no problem. All devices were always aware of each conversation as they happened.

I recently switched to T-Mobile and ported over my ATT number. I can no longer use the iMessage program on my Macs nor can I use the Messages app on my iPad / iPod (okay, iPhone 5 with no cell signal) to text message friends that are not themselves Apple iPhone users. I can only text message non-Apple users by directly using my iPhone 6 running iOS Also, all devices are logged in with the same Apple ID.

I'm uncertain if the change of carriers has anything to do with it, but that's the only significnat change that's taken place that I'm aware of, and correlation always implies causation... right? Right.

How can I SMS/MMS non-iPhone people from my iPad / iPod / Macs?
On your iPhone, I'd try going into Settings > Messages > Text Message Forwarding and then uncheck the switches by whatever is not receiving SMS messages and then check and then re-authenticate them individually, it should only take a couple of minutes.