Smartphone sales will represent 28 percent of all cellphone sales this year, amounting to more than 420-million units sold, according to IMS Research says.

As more smartphones become increasingly affordable, global sales could reach 1-billion by the year 2016 (accounting for about half of all handsets sold), IMS added.

In the first quarter of 2011, Apple’s iPhone alone accounted for 19 percent of total smartphone sales worldwide, up from 16 percent in the comparable period in 2010.

Moreover, while Nokia and Apple dominated the smartphone market at the start of 2011 (together accounting for 40 percent of sales in the first quarter), Samsung is rapidly accelerating its sales profile. The Korean conglomerate now enjoys a 13 percent market shares (an astounding 300 percent jump from last year).

In addition, Nokia’s share has been steadily declining, from 40 percent in the first quarter of 2010, to 24 percent in this year’s first quarter (although it remains the global leader).

Other major players are also seeing their market presence shrink:

RIM is down to 15 percent from 20 percent; while Motorola has remained flat at a 4 percent share.