Check the number before departure
If your Chinese mobile number is used for account sign-in or contact, make a travel plan for that number before leaving mainland China. Ask your own operator whether your subscription remains active during the trip, what keeps it active, whether international or Hong Kong/Macao/Taiwan roaming is enabled for the destination, and whether it can receive text messages there. These are operator- and plan-specific questions; an active Chinese SIM at home does not establish overseas service.
China Mobile is one example, not a rule for every carrier
China Mobile's pre-departure checklist calls out international roaming activation. Its roaming-function page gives channels for requesting activation and says the effective time is shown in the confirmation text after activation. The page directs customers to their local China Mobile service for details. If your number is with another operator, use that operator's current terms instead.
Before you travel, ask your operator to confirm the destination, the roaming status of your actual number, relevant voice and SMS services, plan validity and charges. Record the official support route you can use from abroad. Do not rely on a remembered tariff or assume that receiving a verification text will always work.
Prepare account access as well
- Check which important accounts use this number for sign-in or recovery and follow each provider's official alternative-access instructions, if available.
- Confirm roaming activation through your operator's own account or confirmation message before departure.
- Ask whether the account has a balance, validity or suspension condition that could affect the number while you are away.
- Keep the SIM or eSIM securely accessible. Do not share one-time codes, even with someone offering to troubleshoot your roaming.
If there is no signal abroad
China Mobile's no-signal troubleshooting page says its customers should check roaming activation and, if automatic network selection fails, try manual network selection. Its SMS troubleshooting page treats sending and receiving problems separately. These are starting points for China Mobile subscribers; a device, destination network, plan condition or the sender of a verification message may create a different failure.
Contact your operator through its official overseas support channel if service does not return. If the phone has signal but a specific account code never arrives, also ask that account provider about its verification and recovery options. Do not make a consequential payment or account change on the assumption that an untested SMS will arrive abroad.