Thanks for using Apple Support Communities, Tintino001.
I see your iPhone 6s recently upgraded to iOS 10 is unable to send or receive messages but your iPad can. Let's get Messages working on your iPhone then.
If you can‘t send or receive messages on your iPhone, iPad, or iPod touch -- The troubleshooting for Messages hasn't changed from previous iOS versions. Have a look at this article to make sure everything has been set up correctly.
How to back up your iPhone, iPad, and iPod touch -- If the previous troubleshooting didn't help, this may indicate that the iOS update didn't install on your iPhone correctly. I highly advise backing up your iPhone before you proceed.
Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings -- In order to install a fresh copy of the iOS, you'll need to completely erase your iPhone. You can only accomplish this using iTunes.
The first time through, select "Set up as a new iPhone" when asked. You can log into iCloud if you'd like to sync your contacts to your phone to test with. Activate iMessages on your phone then see if you're able to send and receive messages without having to restart your phone. If it's working like it should again, continue with the next step.
Restore your iPhone, iPad, or iPod touch from a backup -- Use this article to guide you through putting your personal information back on your phone.
Have a great day!
