Boston-based HeyWire now really has you covered when it comes to chatting. Today, the messaging service launched HeyTweets, enabling you to stay connected to your tweeps over SMS for free, and from anywhere in the world.

HeyWire’s core service is that it streamlines and places three different text and chat services into one app: SMS, Facebook Chat and Google’s GTalk. And HeyWire is the only app that allows you to use a real phone number to text any other phone — including group texts to up to 10 people — for free across the globe. Now HeyWire allows you to do the same with tweeting over SMS with HeyTweets.

When signing up for HeyWire you receive a HeyWire phone number—your “texting identity”—and encourages you to send that number to friends. When initiating and sending your first text-to-tweet to 40404 (which needs to be “start”), the service prompts you to reply with your Twitter handle and then password. I had issues signing up thanks to a nasty bug they’re working diligently to fix (since I was a current user I needed to delete the signature line in HeyWire’s settings before Twitter recognized my username).

How does HeyWire allow you to SMS from a real phone number for free? A real phone number and texting costs HeyWire money, but the company serves ads to keep the messaging flying around the world for free. The app even includes push notifications and emoticons (who doesn’t love emoticons?), and just like regular texting HeyWire users can text a friend with any type of mobile phone across 360 mobile operators in 144 different countries.

I first met the HeyWire team at gdgt here in Boston, and more recently received rave review from CNET from their demo at the CTIA conference. “It is HeyWire’s mission to simplify the connections between people, no matter where they are or how they want to connect,” said CEO Meredith Flynn-Ripley in a press release today. “By empowering HeyWire users to Tweet via SMS all over the world, they are sure to never miss out on the latest happenings.”

While HeyTweet seems like a natural extension of the service, as an smartphone user near wifi or connected to 3G, I’m not sure why I’d text-to-tweet within the HeyWire app (and remember all of these command shortcuts) rather than just tweeting for free from a Twitter app. This app seems made for those times when you’re in areas where you get voice, but no data — like traveling in less developed areas overseas, or the boonies of Maine.

Download the HeyWire app for iPhone (their Android and Blackberry apps on the way), or their beta desktop app for PC and Macs. Follow HeyWire on Twitter @goheywire and join their Facebook community for more updates.