The iPad and iPhone need different email addresses for FaceTime and iMessage.
Using FaceTime http://support.apple.com/kb/ht4319
Troubleshooting FaceTime http://support.apple.com/kb/TS3367
The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting
Troubleshooting FaceTime and iMessage activation
Using FaceTime and iMessage behind a firewall
iOS: About Messages
Set up iMessage
Setting Up Multiple iOS Devices for iMessage and Facetime
FaceTime and iMessage not accepting Apple ID password
Unable to use FaceTime and iMessage with my apple ID
For non-Apple devices, check out the TextFree app https://itunes.apple.com/us/app/text-free-textfree-sms-real/id399355755?mt=8
That doesn't help me since I only have 1 email address (and I like it that way), as well as I want my emails to sync up. I could honestly care less about iMessage and I've turned it off on my iPad. However, it somehow turned itself back on and again, I turned it off after I realized it yet again stole my texts. Now, my texts are getting lost somewhere in the airwaves. What is going on?! This alone is making me regret buying an iPad.