Thanks Ira, hmmmm. one person I texted in messages, a sign immediately came up saying was not possible, so I assumed it was a non Apple user.
If I am remembering correctly, if you are texting from a device that does not have cellular (laptop, desktop, some iPads, iPods) then you will not be able to send a text message to a non-Apple recipient. iMessages to an Apple device appear as blue text bubbles once sent; non-Apple text messages show up as green text bubbles. iMessages require at least wi-fi, ordinary text messages go via cellular networks.
So no cellular, no text to non-Apple devices. Now having said all of this, different cell phone carriers may have work-arounds or options that overcome some of these limitations.