Zhangjieqwer SG 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
LatecomerX SG 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.
BangHong SG Singtel have the sms plus function, but you have to pay too.For more information, go to singtel.com.sg