This is what I do for my wife's phone. I have seen people fill up an entire screen (16 icons) with their most frequently called numbers. Plus in Contacts I have a few numbers "starred" so that they are listed under the Favorites tab in Contacts or Phone.
there's also a great aftermarket app called aTAKEphONE that will take your favorites (starred contacts) and assigns a long-press number shortcut to them, so you long press on the number assigned and you get quick dial