I was really surprised to read a BusinessWeek article on the succes of SMS.ac. Especially after reading Joi Ito's experiences with this company a couple of months back.
"Today, that might be a bit hard to imagine. Currently, SMS.ac, the mobile social-networking market leader, claims some 40 million users, only 14% of whom are based in the U.S. Most other services only have thousands of customers, who typically pay a $5 monthly subscription fee. Yet social-networking services are already a major driver in the use of SMS and multimedia messaging (MMS), says Scott Ellison, an analyst with consultancy IDC."