Why can't I send picture messages to someone who doesn't have an iPhone?

I live in the country and only the "E" comes up as opposed to LTE or 4G. So, is there anything I can do to fix this problem?

Me no understand these kinds of things.

I tried looking this up and all I find is to turn Cellular on, which it is. What now?

Also, did anyone upgrade to Mavericks? I just got this message on my MacBook "Upgrade your Mac to the latest version of OS X for free". Is it good? Should I do it?