There has been a significant increase in the number of U.S. mobile subscribers who own a smartphone, with young adults and teenagers responsible for most of this growth.

The latest figures from Nielsen show that between July 2011 and July 2012 smartphone penetration in the U.S. jumped from 41% to 55%.

Overall it is young adults who lead the growth in smartphone ownership with 74 percent of 25-34 year olds now owning smartphones, up from 59 percent in July 2011. However, it is teenagers. between 13 and 17 years old, who demonstrated the most dramatic increases in smartphone adoption. By July 2012, the majority of American teens (58%) owned a smartphone, compared to roughly a third (36%) in July 2011.

Over half (52%) of all Smartphone owners have Androids, over a third have iPhones with Blackberry accounting for 8%.  But when you look at Recent Acquirers, those who bought their phones in the last three months, the proportion of Android jumps to 59% and that of Blackberry shrinks to 3%, which fits in with the age profile of new smartphone adopters.

Nichole Henderson, a Nielsen analyst, said:

“As teens increase in their share of smartphone owners, mobile carriers and manufacturers should consider how to market to this growing group.”

Developers also need to bear the age demographic in mind when deciding how to market their apps.