Are you sure, that it is not recognized? Maybe just the corresponding menu items are missing 
I remember that I specially unlocked the sim and after the initial setup I was able to send and receive SMS but could not make or receive a call. In the Setup, the mobile connection item was present.
After the reboot my operator name was missing in the upper info field and in the Setup the corresponding menu item for mobile connection was also missing. However, using the Phone app I was able to make a call (wasn't able to use country code), recieve a call and with Messages app send/receive SMS. Was not able to switch on the mobile data connection.
And yes - SailfishOS is the most smooth and freshlooking mobile operating system
I remember that I specially unlocked the sim and after the initial setup I was able to send and receive SMS but could not make or receive a call. In the Setup, the mobile connection item was present.
After the reboot my operator name was missing in the upper info field and in the Setup the corresponding menu item for mobile connection was also missing. However, using the Phone app I was able to make a call (wasn't able to use country code), recieve a call and with Messages app send/receive SMS. Was not able to switch on the mobile data connection.
And yes - SailfishOS is the most smooth and freshlooking mobile operating system