One of the standard staples of any half-decent sci-fi is communications and data transfer that Just Works (except when it fails for reasons of Plot), and where everything is compatible (again, Plot aside). Star Wars has comlinks that can communicate with anything, datapads and datacards that are always compatible, and the holonet for real-time sound and video. Star Trek had communicators, and ships could somehow hail each other regardless of what technology each side may be using. Firefly also has some sort of interplanetery communications network that just works. It's always presented as some part of a futuristic society.
The revelation was that actually, current technology can do this and has been doing so for several years. I can phone virtually *anyone* in the world, regardless of what phone system they may be using. I can email a document (in HTML, PDF or plain text), an image (JPEG), sound (MP3), video (MPEG), even arbitary data (comma-separated or possibly XML) to anyone, and their system will be able to open and view it even if it's something completely different. And not just the common ones like Windows, Linux and Macs, but even more obscure systems like Symbian and BeOS can usually handle those formats. There you go - communications and data transfer that Just Works and where everything is compatible (well... almost, but I'll ignore edge cases) is here.
But it gets better. GSM-based cellphones account for over 80% of all mobile phone systems, and there's infrastructure for that in more than 200 countries. Roaming agreements are getting better and better, and if nothing else I can just slot in a SIM card for that country and presto, I have a phone that works pretty much anywhere on land. That's voice calls anywhere (and if you go for a satellite phone like Iridium, that truely is anywhere), and with GPRS I also get decent data transfer on the same network. GPRS is good for upwards of 30kb/s on a good day, which is just enough to stream real-time video as well.
The one part missing from all this is the ability to send a data stream simultaneously with a voice call. Modern tech is close - several of the older voice chat programs support that (e.g. MSN, Yahoo messenger), and modern smartphones can simultaneously make a call and send data, but there's still no actual linkage between them in phones (pleaseremove pointed out the smartphone one, but the solution there is to email the data, using a separate address and a separate connection). That's about the only part of the sci-fi communications that's missing.