You may be in luck, then. The chat-to-SMS functionality that was rolled out a couple weeks ago, then hastily retracted, has been debuted on GMail and is available to most users.
Quick testing here at Mashable shows that most major carriers are supported, but oddballs like me on regional networks like MetroPCS are not serviced by the new capability, and users who message those on unsupported networks will be greeted with the message indicating as such.
To activate the service, simply scroll down under the Settings >> Labs link until you see "Text Messaging (SMS) in Chat" and select Enable and Save Changes. To actually send a message, when you click on the “search, add or invite” blank in GMail, on the pop-up menu will be an option to “Send SMS.” You’ll be prompted to enter their mobile number, which will then send all chats to their phone.
Other than the minor network incompatibilities, it seems like one of the most convenient ways to annoy the crap out of your friends from Google yet!