Why can my iPhone text other iPhones when my phone is disconnected?

Today around 10am my iPhone got disconnected (hadn't paid my bill yet), I went to text my aunt (who doesn't have an iPhone) and the messages wouldn't send, 30 minutes later I texted my friend who does have an iPhone and I could successfully send and receive messages. And as of 9hr later, I was able to text another person with an iPhone. What's up with this? Not complaining or anything, just curious why it's happening.

Well, if you are using Wi-Fi, iMessage will still work. But only with those using an apple product