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P.S. I have also done the telephone missions
(How can you find collecting cars fun?!!!!!!!!!!)
I'm quite certain that collecting the Sunshine Autos cars wasn't necessary to complete the missions.
I haven't played it for quite a while but I vaguely remember having to buy the ice cream business and then getting to a level 50 or something. After that, new mission strands opened up.
If that turns out to be wrong (which I suspect it will), then I suggest you look at a guide.
P.S. I have also done the telephone missions