Due to non-coverage in fixed telephone samples the dual frames combining mobile and fixed telephone numbers are increasingly used in telephone surveys of general population. However, with dual frames we need to estimate the domains related to single and mixed telephone usage. In the simplest case, we usually have three segments: fixed-telephone-only users, mobile-phone-only users and those in the overlap. The exact allocation heavily depends on phone use definition. There, at least two criteria can be used: possession (person has a mobile/fixed phone) and availability (can be reached on a mobile/fixed phone). In practice, various wordings can be applied for possession and for availability question. In this paper, we first explored contemporary dual frame research. Based on that, we generated a meta-overview of question wordings. Next, we address the problem of the corresponding sample and population shares for these segments. With respect to the overlap segment, which tends to be very heterogeneous, we also discuss two additional segments, the mobile-mostly and fixed-mostly segments, referring to persons who might possess certain (fixed/mobile) telephone, but rarely use it (or being unavailable on it). We use empirical data to illustrate the demographic structure and telephone usage patterns in case of three and in case of five segments. At the end we propose possible ways towards standardization of these questions.