The Sony Xperia C has tri-band 2G and dual-band 3G connectivity. Mobile data speeds go at 42.2 Mbps of HSDPA and 11.5 Mbps HSUPA. Only the primary SIM card can be connected to a 3G network and usually this is the SIM card you've chosen for mobile data (you can still make and receive calls on that SIM, don't worry). The other SIM will be connected only to a GSM network. You can opt to use data traffic from the second SIM, but you'll be limited to EDGE connectivity and speed.
Local connectivity is covered by Wi-Fi b/g/n with DLNA and Wi-Fi Direct, so you can easily share content from your phone on a DLNA TV or music player. If a media app supports the Throw function (like the video player), you can use it through the Smart Connect app for DLNA functions (sharing screen, etc.).
There's also Bluetooth 4.0 with A2DP, which can be used for low-power accessories (e.g. sports trackers). There is no NFC support though.
MicroUSB handles the charging and PC connectivity, and there's also USB On-the-go support, so you can attach external flash drives to the smartphone as well. You can connect mice and keyboard, too, thanks to the USB Host support.
The Xperia C comes with Sony's Smart Connect app, replacing the former LiveWare manager. With Smart connect, you can set your device to do a variety of things, like launch an app or set an alarm, whenever you connect an accessory, e.g. a headset or a charger, or at a preset time. It doesn't work with NFC though, which is very disappointing.
Finally, there's Xperia Link, which shares the phone's Internet connection over Bluetooth instead of Wi-Fi. All you have to do is use the camera to scan the QR code generated by the app on the tablet or computer. If you have the Xperia Tablet Z, the app will also display notifications for incoming calls and show full text messages.
The Sony Xperia C comes with Google Chrome as the default web browser out of box instead of the generic Android browser. While the minimalist interface hasn't changed since Chrome launched on Android, the browser is being constantly refined by Google, and this has resulted in one of the smoothest and most powerful browsing experiences we've encountered on a mobile.
At the top there's an URL bar with a refresh/stop button next to tabs and settings. You can switch between tabs with a wide horizontal swipe in either direction.
Chrome runs on the WebKit rendering engine, so underneath the minimalist UI it's basically the same as all Android stock browsers.
Of course, one of Chrome's strengths is its ability to seamlessly sync with the desktop version, using nothing but your Google account. This allows you to open an article on your PC and finish reading it on your mobile phone. It also syncs your bookmarks and favorite sites.
Opening the tabs area reveals a list of tabs which can be closed, again with a left or right swipe. The animation accompanying this action is neat, too. Incognito tabs, which lets you browse without saving history or cookies, show up right next to regular tabs.
A brand new setting is called Reduce data usage and does what it says - Google servers compress the webpage (using Google-developed tech like SPDY and WebP) and send them to the phone. You can check the graph to see how much data you've saved. Unlike Opera Mini, this mode keeps the full functionality of web pages. Also, secure connections bypass the Google servers for privacy reasons.
Also, keep in mind you can use the Small app browser, which lets you surf while doing other things on the large screen. Unfortunately, there's no easy way to switch from Chrome to the floating browser.
The Sony Xperia C comes with the OfficeSuite 7 viewer. OfficeSuite 7 lets you view Word, Excel, PowerPoint, PDF along with plain text files. Just view them though, as you'll have to buy the Pro version if you want editing capabilities as well.