Except they don't -- not quite yet. Word processing and printing can't easily be done from a phone, or even a tablet; the ideal software doesn't seem to have been written yet. Voice recognition remains choppy, as does the answering of "natural language" queries (e.g. SIRI). And, for all its wonders, the smartphone has limited power, limited data capabilities, and is highly dependent on technologies that still, at times, fail.
Of course we can dream! -- check out the Pomegranate smartphone, for instance. But we can also see some definite trends which, if they continue, point to something like a true convergence:
• Cloud computing -- Having content in the cloud makes sense and is already common; the next step would be having one's software in the cloud as well. Ultimately, with the right interface, our hand-held devices would simply be screens, with enough memory and power to handle the influx and outgo of data, caching some to improve performance. Google is already marketing a "computer" of this sort, the Chromebook Pixel.
• Transparency across devices. The idea that, no matter where you are, or what device you are using, you ought to be able to see and access the same materials, and pick up just where you left off, is a crucial step. Amazon's whispersynch is one such; Apple has also built in various elements of synching (such as Contacts) into its devices. But here are still hurdles, chiefly at the level of operating systems.
• Short-range wireless interfacing. In an ideal world, every device would use some common standard, such as Bluetooth, and everything you owned could "speak" wirelessly to every other thing. You might even be able, say, to enter a hotel room and find it already adjusted for your preferred climate, your favorite shows all set to stream, and your documents and spreadsheets instantly available at a touch of a screen. But right now, the standards vary, and issues with bandwidth and interference threaten to make this channel a crowded and unreliable one.