It shows me an error after I try activate iMessage by phone number

See If you get an error when trying to activate iMessage or FaceTime https://support.apple.com/en-us/HT201422. 

Use these support options if you need more help.

Get a call from Apple support to help solve your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362 Be patient. Sometimes phone support is not available.

Apple ID Support https://support.apple.com/apple-id

Apple Support Twitter https://twitter.com/AppleSupport  There may be a wait of an hour or so.

Apple ID account security for country-specific and region-specific help

 https://support.apple.com/en-us/HT204169

If you tried the suggestions above, here are some other things you can try. Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

If necessary

Hard reset.        

Do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.      

If the above doesn't answer your question, would you please translate the screen shot error message into English and post it in a reply?

Thanks for the feedback.