In modern society, a mobile phone number is a foundation of social life and functions as social infrastructure for accessing public support and employment. A survey of users of “Dare Demo Smartphone” on the reasons they became unable to hold a mobile phone number found that about 17% of respondents, or 105 people, were unable to sign a mobile phone contract not because of their own financial situation, but because of family-related circumstances involving parents, spouses, or other relatives. The survey reports realities that are difficult to prevent through individual effort alone, as well as the reasons these situations make rebuilding one’s life harder. The inability to sign a mobile phone contract is often seen as a personal financial problem. However, when respondents were asked about the main reason payments became difficult, a notable number cited “circumstances involving parents or family” (60 people) or “circumstances involving a former spouse or partner” (45 people). The background includes cases where people lent their name to a parent, had their name used without permission, or had contracts managed collectively within the family. In telecommunications contracts, the contract holder is treated as responsible under their own name. As a result, unpaid bills by family members can directly lead to the person being unable to sign a new mobile phone contract. Unpaid charges may arise without the person realizing it and affect their own credit information. Looking more closely at who affected unpaid telecommunications fees, 56 respondents cited “parents or family members, such as unpaid family discount plans,” while 55 cited a “former spouse or partner.” Free-text responses included cases such as: “My parent borrowed money or fell behind on payments under my name,” “Payments were delayed on a parent-child phone plan,” and “My husband had unpaid bills. By the time the information reached me, it was already too late.” Among people who lost access to a mobile phon