A. Not everyone would read your texts because R2 speaks a different language than everyone else, he could read them to you via earpiece.
C. Cars can be adapted to fit a droid slot. Highly unlikely he would get knocked over, also he can electrify himself that way if anyone bumped into him they would get a slight shock.

Also you are over-thinking things too much with this. If full-size R2-Units were available for sale, the world would be different. Also they would run off of the current technology mixed with the technology that is in the Star Wars galaxy. Vehicles would have droid slots to fit the R-Series units. If you actually think about the technology cars have currently, that same technology is similar to the technologies that R2-D2 had. Cars currently can read our texts, give directions, etc… Same thing that R2-D2 could do. Also if Droids were prevalent in the world, things would actually work in their favor. People would be more aware of them traveling around.

Also I could never stop being friends with you over a discussion on whether or not R2-D2 would be a viable replacement to a cellphone.