The population of cellular-telephone-only households has increased rapidly in recent years and further growth is expected. To meet this growing challenge, NORC at the University of Chicago is conducting a Cellular Telephone Pilot study to explore the possibility of integrating cellular telephone only households into the National Immunization Survey (NIS). The effort included focus groups and four surveys of cellular-telephone subscribers during 2007, the last two of which were conducted as experiments for the NIS. We discuss practical issues of survey methodology faced and solved in these surveys, including dialing protocols, call outcomes, respondent compensation, interview length, and the introductory script. The NIS is a nationwide, list-assisted RDD survey sponsored by the Centers for Disease Control and Prevention. Designed to facilitate monitoring of vaccination rates for children ages 19 – 35 months, the NIS conducts approximately 24,000 household interviews annually. The NIS also uses a provider follow-up survey to collect provider-reported vaccination histories of children in sampled households.