Calling / Data, Messaging, Browser
The Nokia Lumia 710 supports T-Mobile's "4G" HSPA+ network, but it maxes out at 14.4Mbps, so it doesn't take full advantage of the network's capabilities. In my area, which admittedly does not offer the best T-Mobile coverage, I was able to record download speeds of 1Mbps on average - typical for many T-Mobile devices. Unfortunately, the Lumia 710 does not have access to the Internet Sharing feature that came with the Windows Phone 7.5 update.
While the Lumia 710 won't impress anyone with its network speeds, call quality was quite remarkable, as the earpiece was very loud and clear and callers were able to easily understand me.
The Lumia 710 takes advantage of the Messaging hub in Windows Phone 7.5 to offer threaded SMS and MMS conversations and Facebook Chat and Windows Live Messenger support. Conversations from social networks are integrated with standard SMS and MMS messages in a fluid and easy interface.
The email app on the Lumia 710 is the same powerful client as on other Windows Phone devices, and it supports POP3 and IMAP accounts as well as having what is arguably the best Exchange support of any platform. As a heavy Gmail user, I do wish that it supported Google's email service better, but for standard email accounts it is excellent.
While Nokia has decided to leave the WP interface and experience untouched, the company has taken an interest in making its own custom apps that offers on the Lumia 710. The Nokia Drive app comes with every Lumia device offering turn-by-turn, voice-guided navigation free of charge. The app is solid and offers accurate directions with the ability to download maps for offline use (better watch that internal storage though - all of North America amounts to 1.8GB of maps). The Drive app could benefit from the addition of a list view of the planned route, so drivers could get an idea of where they will be headed before hitting the road.
The other apps included with the Lumia 710 are more forgettable, though sports aficionados might enjoy the ESPN app built specifically for Nokia devices. T-Mobile made a point to pre-install a number of its own apps, including an account management app, T-Mobile TV, and the TeleNav GPS navigation app. The TeleNav app requires a monthly subscription, so owners are probably better off with the free Nokia Drive app.
The Windows Phone Marketplace is growing, and it just eclipsed 50,000 apps, but it still is far behind the Android Market or iTunes App Store in terms of apps available. On a more subjective note, the apps that are available on Windows Phone don't seem to be as fully featured or high quality as on the other platforms, but your opinion on that might differ from mine.
The Nokia Lumia 710 features the same impressive Internet Explorer 9 for Mobile browser as found on other Windows Phone 7.5 devices. It is quite fast, even with a lousy network connection, and supports multiple windows. Some may take issue with the lack of support for Adobe Flash Player, and many mobile web pages have not yet been coded to work well with the browser, but it does have potential to be something good in the future.