PHONE is a dichotomous variable in IPUMS-USA. In the 1960 and 1970 censuses, a "yes" response on the PHONE variable meant respondents had access to a telephone either inside or outside their housing unit; thereafter, "yes" meant that the telephone was inside the housing unit. The 2000 census and the ACS specifically asked about the availability of telephone service, not simply the presence of a phone. Researchers should combine IPUMS-CPS categories 2 and 3 to achieve comparability between IPUMS-CPS and the 1960 and 1970 censuses in IPUMS-USA. For later census years and the ACS, category 3 in IPUMS-CPS is comparable to a "yes" response in IPUMS-USA.