The T-Mobile Sonic 4G Mobile HotSpot, though fast enough for most Internet applications, wasn't the fastest mobile router in terms of data speed I've seen. In fact, in my testing around San Francisco, on average, it was actually slightly slower than the previous model, the T-Mobile 4G Mobile Hotspot ZTE MF61, which came out a while ago. Still, overall, it makes a very good investment.
First of all, it comes with a very strong battery that lasted up to 8 hours in our testing, which is about 2 hours more than what T-Mobile claims. A mobile router's battery life depends a lot on how much you use it on the go. The good thing about the Sonic 4G is the fact that it can go in and out of standby mode very quickly without any user interaction. While other mobile routers need to be "waken" by a press on the power button, the Sonic seems to wake when there are data requests. And the router can stay in standby mode for days on a full charge.
Secondly, the router looks great and is very compact. It comes with a tiny OLED display that shows all the important information: battery life, number of connected Wi-Fi clients, cellular network, and signal strength. The router includes a microSD slot to host a card and share data stored on it with a computer it's connected to, or with Wi-Fi clients connected to it, in a miniature yet effective network storage option. Users can also send and receive text messages via its Web interface.
T-Mobile offers three data plans with the router that cost $80, $50, and $40 per month with data caps of 10GB, 5GB, and 2GB, respectively. While there's no unlimited data plan, you can still use the Sonic 4G when the monthly allowance runs out, but the router's connection speed will be reduced significantly for the rest of the month. The router itself costs $100 after rebates and with a two-year contract.
For more information about its performance and other features, check out CNET's full review of the T-Mobile Sonic 4G Mobile HotSpot router.