Need help transferring my number

Hi so this is my setup.

I have a Samsung handset that takes two sims.

My main sim is with O2 and that’s the number all my friends have for me.

My second sim is with Smarty and that I use for the data.

I want to finish with O2 and just use Smarty for everything…

I have now got a pac code from O2 and I understand the process I have to do through my dashboard

Sorry to ask silly questions but just to double check the process outlined here in the help section would see my Smarty phone number no longer work as  my previous O2 number goes on to the Smarty sim card so everyone can contact me still……then the O2 simcard becomes obsolete?