Actually, my fear was that accessing mozMobileConnections could be slow and I was wondering if we could not make the whole init asynchronous, but I measured it and it's not slow at all (about 13 ms).

I'll finish the patch in this form and I'll see what I do with the Settings refactoring. It's maybe not useful because when we use the mmsSizeLimitation and active/nonactive sim we should have the init finished for a long time already.