Wi-Fi texting on the iPhone 5?

What's the difference between the blue and green backgrounds on texting. If the blue means I'm connected to Wi-Fi, does that mean I won't be charged for texts I send out?

I have to pay 15c per text message on my Verizon plan.

Blue- IMessage
Green- Regular Message

  • Why isn't my iphone texting other iphones through imessage? It's updated and so is the person I'm texting. I'm able to text some iphones but not other ones. Even iphones that are new text through the SMS thing. Why?
  • Texting notification to the person I'm texting? How do I change on my iPhone 5s so the person I'm texting doesn't see that I'm texting them with the bubble
  • Texting in class with iphone? When school starts, I won't have a class with some of friends that are in the other grades and the teachers just explain the subjet then when your done with your work they let you talk while they sit and grade papers -thats when i txt but i need new techniques becuz txting in my pocket is noticeable-.- and if you say not to text in class your just wasting your time Plus i bought a black hoodie for when school stars and my iphone has a black case does that make it less noticeable?
  • Is texting or calling from iPhone to iPhone free if you're in a different country? I live in the US And I'm going to Sydney, Australia for 3 weeks in a little while but I'll only be 17 when I go with one of my friends and I wanted to make sure I could communicate with my mom. There aren't many hotels I can find with free Wi-Fi or even Wi-Fi in general. The hotel we're probably going to stay in only offers wired. Both my mom and I have iPhone's so if we text or call on the cell phone data (I have Verizon) will my phone bill price be crazy high?