My friend was a soldier in the National Defense University and was assigned to a security company. He said there was a telephone in the dormitory, but he didn't call for three weeks. Worried. How to contact him? Here are some possible contact information:

1. Try to contact by phone: If a friend's family or relatives have a phone number, you can try to call him directly. Please note that he may not be able to answer the phone due to training or confidentiality reasons.

2. Write a letter: If he doesn't have a phone or is inconvenient to answer the phone, you can try to write to him. Please send the letter to his dormitory or school and wait for a reply.

3. Contact through other friends: If possible, try to contact him through his other friends in National Defense University. Please note that military secrecy regulations may restrict communication content.

4. Online search: You can try to search the official website or social media account of National Defense University to see if there is any information or contact information about the dormitory phone.

5. Consult National Defense University: If all the above methods fail, you can try to contact the Admissions Office of National Defense University or relevant departments to ask if there are any regulations or suggestions on dormitory telephone.

It should be pointed out that communication in the army may be restricted because it involves confidentiality and security issues. Therefore, successfully contacting your friends may require some patience and understanding.