Is my iMessage set up weird?

So I can text and Receive texts from numbers that are not with iMessage without Wi-Fi or cellular data, but I never Receive or never could send messages to my two friends who have iPhones with iMessage or my sister who has an iPod with iMessage. I need either Wi-Fi or cellular data to do so. Why is this? Can I fix this?

Normal texts from numbers that are not with imessage are sent thru carriers (ie. You have to pay for the text), imessage uses Wi-Fi or cellular data instead of using carrier network, that's y you are not able to send messages thru imessage with out Wi-Fi/cellular data.