Gmail sigue mejorando y en USA (pero con intención de llegar a más países) se pone en marcha la mensajería SMS.

We're just trying it out for cell phones in the United States right now, but you can send texts to your friends with US phone numbers from anywhere in the world. You can start by just typing a phone number into the search box in the chat window on the left, then select "Send SMS." You can also select the contact you want to SMS first and then add their phone number.

Link