Perhaps it was too good to last. Although it has been nearly 30 years since the first commercial cellular-phone network was launched, advertisers have yet to figure out how to get their messages out to mobile-phone users in a big way. There are 2.2 billion cell-phone subscribers worldwide, a total that is growing by about 25% each year, according to the Mobile Marketing Association (MMA). Yet spending on ads carried over cellular networks last year amounted to just $1.5 billion worldwide, a fraction of the $424 billion global ad market.
