In the 1980s, mobile telecommunications was, by some accounts , a wilderness. Along came Short Message Service (SMS). Many thought that SMS would be most useful for things like sending a message to a user saying that she had received a voicemail, and few imagined the extraordinary explosive growth of person to person short messaging. Initial growth of the service though was slow - in 1995 an average of only 0.4 messages per GSM customer per month  were sent. But, by 2003, there were apparently  4.2 million active users, and "texting" had entered popular culture. Mobile phones were not perfect for SMS, but the enforced short message size and poor keyboards created an environment where a new language flourished .
With person-to-person calling and text messaging, the mobile environment created a powerful social networking effect.
By contrast with the spare interface presented to the SMS user, modern social networking sites provide sophisticated user interfaces and large numbers of graphical images and other rich media content. Such things are inevitably better handled by computers, with faster processors, relatively large screens and a full keyboard, than by mobile phones.
Is a "mobile social network" nowadays then simply a Web-based social network interface displayed in the Web browser of a mobile phone, or is there something more? How do we engage the still-growing number of people who are more familiar with the mobile phone than they are with the Web?
Phones, mobile and fixed, have historically been person-to-person communication channels - they have not been multicast or “publishing” type communication channels. These are substantive differences which have strongly influenced how mobile phones and the Web have been used for social networking. There are legal implications that arise from these differences such as:
Mobile phones also have obvious limitations, such as a small screen size, limited keyboard and often intermittent or poor network connectivity.
Increasingly, however, so-called "smart-phones" have overcome previous limitations of processing power and storage, and provide a powerful computing environment. In addition, mobile phones now provide several advantages over their larger and more stationary computing device cohorts.
Through the use of haptic  technologies, the sense of touch can be applied to social networking. Currently, most interaction in social networking is through visual feedback. By using haptic feedback it is possible to provide interaction through touch. Apple's iPhone and other touch-screen phones already provide opportunities for such experimentation. A user interface combining visual interaction with tactile interaction may become both more immersive and more subtle - more socially appropriate.
My mobile phone is always with me. Through its GPS device, it knows quite precisely where I am. It's my music player, so it knows what music I am listening to. This presents both opportunities and challenges. Since a telephone number is a relatively good identifier - it is linked usually only to one person, there are privacy implications of supplying information linked to that identifier, such as geolocation coordinates, or listening habits. As such devices add features, the phone becomes a more complete repository for personal data linked to a single individual.
As mobile devices become more full-featured, and provide a more complete user interface, there are more opportunities to immerse the user in an environment where the "real" and virtual worlds of the user are linked.
For example, using Semacode  or similar technology it is possible for a mobile phone user to photograph a barcode placed on a real-world object, and have that photographed barcode be decoded as a URL, whose associated Web document will then be opened in the phone's Web browser. Applications such as Wikitude  where the phone GPS and camera alone (without recourse to barcodes) provide an even more stunning glance at the future of augmented reality.
In contrast to the increasingly sophisticated capabilities of mobile phones, the fundamental architecture of the Web has not changed much over the past 10 years.
Existing social networks usually employ a "hub and spoke" model, where the website is the hub of all activity within the network, and where there is a "client" and a "server". Since all traffic must pass through the hub, that site may become a bottleneck. Furthermore, each transaction must pass up one spoke to the hub, and then down another spoke, when the people interacting may be much closer to each other (in network terms) than either is to the hub site.
Mobile phones have become quite sophisticated in the features they provide, and offer serious processing power to software applications. There is the opportunity to create an architecture that distributes the load to the devices sitting in our coats and pockets, rather than solely on massively scalable Web sites. Such an architecture would require better interoperability between social networking sites and mobile devices than we have today, and should remove any dependence on an "always-on" network connection.
The multiple-radio capability of some phones (Bluetooth, NFC, WLAN and GSM/GPRS) allows the formation of a social "web of trust"  where people physically co-located can "connect" using a near-field radio, and later access each other's phones over the Internet, based on the initial connection of a local radio . This allows the trust that comes from seeing each other to be extended into the virtual world, where we often cannot see each other.
Mobile social networking involves more than simply replicating existing PC browser-based social networking interfaces in a mobile environment. Social networking systems could benefit from some of the context brought by the technology provided in such personal devices, but must become more aware of the social responsibility inherent in taking advantage of these features. Integrating person-to-person calling devices into a socially-networked Web is not the same thing as displaying the socially-networked Web on a mobile phone.
During the next three to five years industry analysts predict another billion new mobile phone users. When we bring Web-based social networking to mobile phones and these new users, it might be useful to consider that most people on the planet have much more experience with phones than the Web.