How do I send messages from iPad to non apple devices?

Good old fashioned e mail. I message only works to other ios5 devices.

There are a handful of apps in the store that act like text messenger replacements. Read the reviews to pick the one you want. There is no way to do it without a third party app.

you need an app for that. search the app store, there are plenty out there...

Go to the App Store and get Text Free (a free app).

Found a good article explaning why the iPad doesn't send texts over iMessage the way you would think. Turns out that the iPad isn't a phone and doesn't use 3G or Wifi the same way a phone would so you can't really send texts from iMessage on your iPad the same way you can on your iPhone.

http://blog.chron.com/helpline/2011/12/sending-text-messages-from-an-ipad/