1. Local military service registration offices: there are military service registration offices in every region. You can go to the local military service registration office and provide relevant identification information. They can check military service registration's cell phone number for you.
2. Police station: You can also consult the local police station. They often have information about military service registration when handling household registration-related business.
3. Inquiry websites: Some websites related to the military and the government provide inquiry services for military service registration. You can try to query military service registration's mobile phone number on relevant websites, and you need to provide relevant identity information.
Please note that different countries or regions may have different policies related to military service registration, and the above method is applicable to China. For information about military service registration in other countries or regions, please refer to the regulations and consultation channels of relevant local institutions. For further information, it is recommended to consult the local military service registration office or relevant institutions.