Currently Being ModeratedSep 13, 2013 1:16 PM (in response to lburech)
If the bubble was green, the message must have gone by SMS. Macs have no direct SMS capability.
That other person either does not have an Apple iPhone, has chosen not to register the phone number with iMessage, or did not have an internet connection active at the time of your experiments.
There are services that claim to allow non-SMS devices to send SMS messages. I've never tried any of them, so I don't know how well (or even if) any of them might work.
Currently Being ModeratedSep 13, 2013 3:40 PM (in response to lburech)
SMS is a proprietary protocol that is phone only. Nothing that can be done about that on the Mac.
Fortunately there are iMessages which work on both the Mac and on iOS; that's an Apple-developed protocol.