SMS is cheaper considering the battery of your mobile phone. Receiving SMS on a regular GSM-phone does not add much to the power drain. Compare that with an ope

SMS is cheaper considering the battery of your mobile phone. Receiving SMS on a regular GSM-phone does not add much to the power drain. Compare that with an open TCP-Connection to receive emails (or XMPP-messages). Or worse with polling for email. And you can reach about anyone with a cell phone with SMS. Most people to not read all their email on the go.