I just changed from Swisscom to Orange yesterday.

I was going to ask how to change the speed dial in the phone app, but just chanced upon the solution. Searched google, youtube and here for a bit and didnt find a direct answer, so in case anyone else wants to know:

Phone *5005*86*004178xxxxxx# where of course the last digits are YOUR number in international format.

It feels like it does nothing (theres no voice prompt and you dont even know it connected), now try the speed dial. Et voila.