The latest version of the iPhone OS (iPhone OS 4) which runs iPhone, iPod touch, and iPad will ship this summer -- first for iPhone and iPod touch, and, in the fall for iPad.
Starting on June 7, Apple's annual Worldwide Developer Conference (WWDC) takes up the tools and features of Apple's hardware and software. If you look at the schedule, you'll see exactly what Apple has done: the core and foundation functionality of Mac OS X (they are actually called Core and Foundation) are the basis for the Mac, iPhone, iPod, iPod touch, and iPad. There's been very little if any retrofitting or fiddling -- this design has remained intact since the mid 1990s.
While telephony in the form of faxing was part of the Mac OS X predecessors (Nextstep and Openstep), it would be a stretch to say that it was all done to culminate in iPhone. My guess is it was done to be able to take advantage of any new features that came along. Some features are added and some are removed, but the architecture has been proved. As a case in point, faxing (in the form of NSPrintFaxJob, a destination for a print job) has existed for years (it's on page 416 of my book, Rhapsody Developer's Guide, published in 1997). It was only deprecated in Mac OS X v 10.5 (the current version is 10.6). The ability to generate PDF files from documents and then to email them provides the functionality of faxing without the fuss, and we've got PDF generation in iPhone OS and Mac OS X (in Quartz).
The possibilities of iPad have barely been explored. It's a great device for reading and consuming media; it's also a phenomenal tool for exploring data (and Apple has given us the tools with Core Data and the various Interface Builder tools to manage lists and other data structures). Most of this has been there for years -- many years in most cases.
Now it's time for developers, end-users, designers, and artists to put all those existing software pieces together into new structures.
And there are plenty of us who have our sleeves rolled up. But there's room for many more.