I have found one feature of gmail. You can send SMS from gmail (google email) like chatting. Especially, when you are roaming. http://www.messagingbay.com/smsxmpp.jsp?navi=27
It's not a feature of Gmail, but a SMS gateway provided by a third-party that is able to receive messages as e-mails and send them out as SMS messages. And it's not free.
Singtel have the sms plus function, but you have to pay too.
For more information, go to singtel.com.sg