This is probably an embarrassingly noobish question.

I sent a standard SMS text message from my iPhone 6 to a colleague's iPhone, who mentioned that my message was green and not blue, and that meant I hadn't activated something or wasn't using the right app to take advantage of iMessaging.

Currently I don't use apps beyond what came with my phone. To send SMS text messages I use the green callout balloon button that's near the phone button.

[![enter image description here](https://i.sstatic.net/z6SuB.png)](https://i.sstatic.net/z6SuB.png)

My colleague said I could save money by using iMessage instead of paying for each SMS text message. I countered by saying that if it's not SMS then that means I'd have to keep my phone connected to the internet 24/7 to receive messages and I don't do that. 

My colleague then said something like *it does but doesn't use SMS*, so I wouldn't have to maintain an internet connection 24/7 to receive prompt iMessages and yet would not have to pay for SMS messages when I did.

A quick search turns up plenty of tutorials about how to use iMessages but so far I have not found a clear *and concise* explanation.

Is it possible to explain *in a few clear sentences* how the messaging functionality works on my iPhone6 and when internet is used and when traditional SMS messages are used? For example:

 - Does it check first for an active internet connection on the sender's phone?
 - Does it also check if the recipient is also connected to the internet?
 - Could a message go out as an iMessage and then not be delivered even though the recipient could have received an SMS text message?