Microsoft gives you the option of encrypting all traffic passed to and from the phone. You can also turn the VPN on or off manually, or just set it to trigger when certain domains or sites are accessed.
My first VPN experience ended quickly. I tried entering the IP address and password for our VPN myself, but I wasn't able to get the VPN to connect. I'll be checking with our IT department, and you may have better luck if you do the same initially.
One nitpick: When editing an active VPN profile, selecting the advanced options brings up a toggle: "Don't use VPNs on company Wi-Fi." The default setting is Off--a double negative that's needlessly complex.
Improved Xbox Music
Xbox Music fans will probably be happiest that Microsoft hasn't forgotten about them, promising an updated Xbox Music app. Surprisingly, I didn't notice any difference--but they again, I don't subscribe to the service. (I use Slacker myself, especially on my T-Mobile Android phone, where playing music doesn't count against my data cap.) It would be lovely if Xbox Music for Windows Phone allowed me at least to play back algorithmically-generated "radio" stations.
Finally, there's Cortana, which Microsoft says includes new natural-language capabilities. That's a bit difficult to test, although a new "do an impersonation" request prompts Cortana (voiced by actress Jen Taylor) to run through a few lines. Cortana has also been adapted for the UK and China, among other regions. (At least on my phone, however, you can't ask Cortana to speak in an English accent, yet.)
The performance drag on my phone could be a subjective impression, and my VPN problems may be easily solved with a bit of help. Your mileage with Windows Phone 8.1 Update may vary. In any case, there's little reason not to upgrade. Just don't go in expecting too much.
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