What do I do if my screen says iPhone Unavailable?

I got locked out of my iPhone last night and I couldn't get back in. I tried every number I thought would be right and then after one last try, it said 'iPhone Unavailable' on the screen. I looked up how to unlock it and erase it if I had too but I couldn't do anything with it. it stayed the same, saying the same text on the screen and not changing at all. I really need to get back into my phone as I'm going out of the country for a while, and of course I'll need my phone. Apple really needs to make it easier to get into their phones, this is ridiculous.