The hallowed Texas Instruments BA II Plus financial calculator, selling for $US30 at Walmart, is now a reasonably identical iPhone app, selling for AU$18. But TI says that fears of cheating will keep standalone calcs selling for years to come.
TI's PR person told GigaOm that her husband, a realtor, uses the real live calculator at the office, but would use the iPhone app in the field, so he doesn't have to carry extra stuff. I'd think sooner or later, the app, with its ability to relabel buttons clearly and instantly, would eventually win out. At least until a totally organic touch version that can do the same calculations comes out. (Why stick so religiously to these old forms?)
The cheating argument, however, is valid: TI suggests that people still buy actual calculators because test givers prohibit students from whipping out their iPhones. So there's at least one strike against well-executed convergence. [GigaOm; iTunes Store link]