http://www.pewresearch.org/2015/11/18/advances-in-telephone-survey-sampling/

Telephone surveys face numerous challenges, but some positive developments have emerged, principally with respect to sampling. Companies that provide telephone samples have developed several products that have the potential to improve the efficiency of surveys in both the landline and cellphone frames and allow for more accurate geographic and demographic targeting of calling in the cellphone frame. A number of tests have been conducted with these products, and the relative costs and benefits of each are becoming clearer. This report describes some of these innovations and presents the results of experiments conducted with each of them.