Cannot send text messages from Mac Messages app

The messages app on my MacBookPro will not send messages. It only receives messages. Every time I get any message on my iPhone, the messages app pops up on the computer, but then it refuses to let me reply to them. I always get "Now Delivered" with the "i". I click on the "i" and click "Try Again" but that always fails.

I've tried deleting all facetime keys out of my keychain, but that didn't work (with numerous reboots in between)

I've tried deleting the iChat and iMessage plists out of ~/Library/Preferences, with numerous reboot. No luck.

Has anybody gotten Messages to work consistently on a MacBookPro?