IMessage problems, sending as text?

My setting for imessage is turned on but whenever I send a text to another person with an iphone it shows up with an red exclamation point next to it, meaning it isn't delivered and then it sends as a text again. Then when the person texts me back it says that it is imessage until I reply. What is this? Any suggestions on how to fix it?

My iPhone won't let me use Wi-Fi?

My iPhone won't give me the option to turn on Wi-Fi whenever I go under settings to Wi-Fi it is grey and when I try to click to turn Wi-Fi on it won't let me.
I tried resetting network settings and it didn't do anything
What do you do? My iPhone is up to date on everything