When considering a change of mobile phone systems there is a lot more to it than making telephone calls, in fact making phone calls is almost the least important aspect of a mobile phone.
Looking at my logs it is clear that I make less than a handful of actual telephone calls a month; I mainly use messaging apps such as Signal for example.
The main use of my phone appears to be as a host for several apps and a method for connecting them to the internet using either mobile data of wi-fi. It is the infrastructure of network connected services such as email, messaging, cloud storage, photos, media, calendar, synchronisation etc., that are embodied in the mobile phone.
So while I wait for a suitable platform on which to hang all these systems I am trying to create a portfolio of independent or self hosted services to replace them. Then, when I can make the change everything I am used to is available and ready to go.