What does this mean? Imessage

When I try to send a message to a new number (my friend) it changes from message to imessage meaning they have an iphone. So when I actually send a message it doesn't show delivered or anything, then I waited like 5 minutes and it finally converted to text message. I tried calling their number but it says the number you're trying to reach is unavailable. But then I try to send them a message again (since I don't have them in my contacts) and it goes from regular message to imessage again. Does this mean they have imessage but no phone line or what? Technically my messages aren't getting sent either, right?

They probably do not have a phone contract/plan but use iMessage as a method of communication. Or they can just have an iPod.