Before changing your phone number or giving up the old one, relink bank, payment and social accounts to the new number; do not just let the old SIM be suspended for unpaid bills

No charge. Change the linked number separately for each account, and contact the bank to update the number it has on file. With many regularly used accounts, this may take one or two hours. It is easy to miss an account, especially one you rarely use.

China's Telecom Service Specifications set a minimum 90-day freeze for mobile numbers, meaning the period between cancellation and reactivation. After 90 days, a cancelled number may be assigned to a new user. The Ministry of Industry and Information Technology's first-quarter 2025 service-quality notice said users could use the three carriers' apps to access 二次号码焕新, a service for refreshing reassigned numbers. A new holder of a previously used number can use it to unlink internet accounts registered to that number before their own subscription began. The second-quarter 2026 notice said the service covered 258 commonly used internet applications and had received more than 850 million application-unlinking requests. The fact that new holders need this service shows that the previous holders' accounts can remain linked after reassignment. In 2024, customer-service staff from the three major carriers told People's Posts and Telecommunications News that after cancellation, new users could still use SMS codes to access accounts registered by previous users. They advised unlinking apps such as Alipay and WeChat before changing or cancelling a number and promptly updating the phone number held by banks. This applies nationwide in China.

信息产业部 (2005). 电信服务规范（信息产业部令第 36 号，附录 2 第 2.1.7 项）. https://www.miit.gov.cn/zwgk/zcwj/flfg/art/2020/art_0cff75e226764dc7b811cd4e954415c5.html；工业和信息化部 (2025). 关于 2025 年第一季度电信服务质量的通告（工信部信管函〔2025〕85 号）. https://www.miit.gov.cn/jgsj/xgj/fwjd/art/2025/art_1bcadc32bf8141a8b616db8eaadba2e9.html；工业和信息化部 (2026). 关于 2026 年第二季度电信服务质量的通告（工信部信管函〔2026〕258 号）. 内蒙古自治区通信管理局转载. https://nmca.miit.gov.cn/xwdt/xydt/art/2026/art_2f6af9120a064a6784557cdefbf1c5be.html；李玥 (2024). 三大运营商提醒用户：变更或注销手机号码前务必先解绑. 人民邮电报，西藏自治区党委网信办转载，2024-04-08. https://wxb.xzdw.gov.cn/wlaq/aqdt/202404/t20240408_456634.html（网页存档 https://web.archive.org/web/20250414055537/https://wxb.xzdw.gov.cn/wlaq/aqdt/202404/t20240408_456634.html）

First use 一证通查 2.0 to check how many accounts are linked to the old number; see Item 11 (SIM cards registered in your name). Update bank and payment accounts first, followed by social accounts, and close accounts you no longer need. Do not cancel the old number immediately afterward; keep it for one or two months to catch verification messages from accounts you missed. This is the author's experience. The claim that a new holder can use verification codes to sign into old accounts comes from carrier customer-service statements in media reports, not an official bulletin or judgment. For what to do after someone signs into your account, see Item 6 (signed-in devices). Before replacing or selling a phone, separately sign out and restore factory settings; see the note to Item 8 (delete your personal information). This is grade C because no study estimates how much loss relinking prevents. The benefit magnitude is judged medium. The beneficiary is you.