mobile ad hoc social networks, which are the result of individuals using personal communication technologies to coordinate collective action.
A concept, a book, and a blog.
Concept introduced by Howard Rheingold in a book of the same title:
"Smart mobs emerge when communication and computing technologies amplify human talents for cooperation. The impacts of smart mob technology already appear to be both beneficial and destructive, used by some of its earliest adopters to support democracy and by others to coordinate terrorist attacks. The technologies that are beginning to make smart mobs possible are mobile communication devices and pervasive computing - inexpensive microprocessors embedded in everyday objects and environments. Already, governments have fallen, youth subcultures have blossomed from Asia to Scandinavia, new industries have been born and older industries have launched furious counterattacks.
Street demonstrators in the 1999 anti-WTO protests used dynamically updated websites, cell-phones, and "swarming" tactics in the "battle of Seattle." A million Filipinos toppled President Estrada through public demonstrations organized through salvos of text messages." (http://www.smartmobs.com/book/book_summ.html)
"Smart mobs have been documented in a number of different contexts. An exemplar of smart mob behavior is the 2001 toppling of the Estrada administration in the Philippines when citizens were urged to take to the streets wearing black (Rheingold, 2002; Bociurkiw, 2001). A more recent example is the French race riots of the summer of 2005 during which police revealed that rioting teenagers were using the internet and short message service (SMS) messages to coordinate attacks (Smith, 2005). Likewise, during December of 2005 Australia had to contend with youth using SMS messages to instigate and coordinate violence aimed at individuals of Middle Eastern descent in response to the beating of two lifeguards (BBC, 2005)." 
Discussion on Smart Mob formation
All excerpts from 
Treshold Theory of Social Action
"One explanation for the creation of smart mobs is the threshold models of collective behavior. Threshold models propose that individuals have a particular threshold at which they are willing to engage in collective action (Granovetter, 1978). Threshold models attempt to explain why individuals may be willing to participate in actions collectively that they would not be willing to participate in alone. The argument hinges upon individuals conducting a cost-benefit analysis which weighs the rewards of engaging in the behavior against the possible repercussions. The more people that choose to participate in particular actions the less likely an individual will be held accountable for their behavior. Some individuals require very few individuals to participate prior to joining in, while others may wait for a majority of the population to engage in a behavior before to taking action. Furthermore, since the threshold is simply the point in which an individual chooses to engage in a behavior two individuals whose thresholds are the same may not be politically identical, as reflected in the popular expression strange bedfellows(Granovetter, 1978, pg. 1422). In short, individuals do not have to share the same motivation to engage in a behavior, they merely must have their threshold level met.
Although the threshold theory holds that individuals need not share an ideology for collective action, Ling (2004) notes that these social aggregates [smart mobs] function as a unit so long as there is a shared ideology and a common sense of strategy, and so long as there is a focused easily communicated form of interaction. (pg. 187)"
Social identity deindividuation theory
"rather than individuals merely having a threshold that must be exceeded in order to take action, individuals in smart mobs may require a shared sense of identity. Social identity deindividuation theory (SIDE) was developed to explain online group interaction through people's identification with social identities. Its basic tenet is that text based environments, such as the internet, served to limit nonverbal cues so that individuals are deindividuated (Walther & Parks, 2002). Deindividuation is the loss of self-awareness and critical evaluation of actions as a result of the anonymity created by group scenarios. For example, larger group sizes have been found to facilitate behavior that contradicts societal norms such as taunting suicides to jump or joining a lynch mob (Mann, 1981; Mullen, 1986). Furthermore, anonymity under conditions of deindividuation has been found to result in salience given to contextual cues concerning how to behave (Johnson & Downing, 1979; Spivey & Prentice-Dunn, 1990). Considered in the context of communication media, it has been found that different media may result in the personal and social attributes being more or less salient. For example, when individuals were individuated by being placed in the same room as one another during interaction they were less likely to comply with group norms and more likely to exert an independent identity (Postmes, Spears, and Lea, 1998). Deindividuation in turn affects whether interpersonal or intergroup differences matter during interaction (Postmes & Baym, 2005).
When people cannot individuate others they are forced to rely on contextual cues that indicate the social identities of group members. Social identities do not just consist of an individual's understanding of a group or social category, but are a shared conception within a group of the defining features of group membership (Postmes & Baym, 2005). Along with norms, social identity can mold group action as a result of social identification and social categorization. Social identification is the internalization of a social identity resulting from long term identification with a particular group and so that group norms are subsequently adopted as personal norms. Conversely, categorization is the result of social context increasing the salience of particular social categories. In short, rather than relating to others as individuals, SIDE theory proposes that, in conditions of limited information and subsequent deindividuation, people relate to one another on the basis of group membership.
Initially, it seems unlikely that SIDE theory can provide an explanation of group behavior in smart mobs. First, individuals who receive a message calling for a smart mob to coalesce may know the sender. After all, the primary way that smart mob messages spread is via forwarded messages sent to multiple receivers in the sender's address book. The key rests in the receiver's media literacy. It is common for received text messages to be forwarded to others in some cultures, for example, teen cultures of Asian and Scandinavian countries. If individuals perceive the message as originating from the immediate sender, then SIDE effects probably will not be observed because too much individuating information is known about the sender. That is, the receiver is more likely to relate to the sender on an interpersonal level rather than a group level. However, if the receiver interprets the message as a call for action as having not originated from the immediate sender then it is possible that they will identify with the message on a group level and respond to the cues embedded in the message."
Small World Theory
"Small world networks have important implications for the formation and function of smart mobs. Small world networks help explain how smart mobs form quickly. Milgram's experiment shows that human social networks are, or at least approximate, small world networks. Smart mobs are initiated via text messages sent to multiple individuals in the senderâs address book and, therefore, can be considered a subset of an individual's social network. Still, a majority of people whom the immediate sender of a smart mob SMS knows are likely not included in his address book. This limited list of contacts still may be sufficient to result in a small world network. Although lower link density between individuals in the network might inhibit the spread of an SMS, the nature of SMS technology, which forwards of the messages to large groups of people quickly, could counteract this by allowing for the messages' quick and efficient transmission. There are currently approximately 2 billion mobile phones on the planet and many individuals who do not have access to other forms of new media, such as the internet, that allow many-to-many communication own mobile phones (Gunn, lecture). Such was the case in the Philippines during the 2001 protests against President Estrada. Much of the population lives in poverty and SMS provides a cheap, convenient method of communication (Bociurkiw, 2001). Although mobile phones were far from ubiquitous, small world social networks were likely a decisive factor in allowing messages calling for protest to quickly spread." 
Website of the book at http://www.smartmobs.com/book/book_summ.html
Three-part presentation at the O'Reilly Conference.