U301 ($50, ) modem, it's a perfectly acceptable replacement in Sprint's lineup.
The 250U looks like an Internet lollipop. It's a metal USB stub with an 0.6-by-1.9 inch circular disc on top and two blue lights to indicate whether it's in 3G or 4G mode. A removable cap reveals two external antenna jacks, which is pretty exciting for people who like to boost their signal. The modem gets warm during use, but not uncomfortably so.
With the Samsung Epic 4G ($199.99,) and HTC EVO 4G ($299.99,) offering wireless hotspot modes and tethered modem capabilities, you have to ask: why get a modem anyway? Road warriors know one answer, of course; many businesses will pay for data contracts for their mobile workforces but don't want to buy everyone phones. But there's also something to be said for spreading your battery-draining uses over several devices, and the modems tend to get much stronger 4G signal than the phones. In a stone building in Philadelphia, I could still get strong (-65 to -70 dBm) 4G signal on the dedicated modems while my 4G phones wavered in and out of 4G coverage.
I compared the 250U to Sprint's earlier U301 modem in 3G mode in New York City and in both 3G and 4G mode in Philadelphia. Speeds generally ran neck and neck. The 250U was faster on one category of 4G downloads, but I wouldn't draw broad conclusions from that. I'd expect similar performance in large part because the two modems use the same chipsets—Qualcomm's QSC6085 on the 3G side and Beceem's 250 on the 4G side.
That said, the 250U has several advantages over the earlier modem. It swivels and rotates to fit a range of USB ports. Most notably, it sets up more quickly. My U301 modem was plagued by long initialization delays where the PC would reboot the 4G chipset and then search for the network. The 250U comes up in a few seconds. That's a nice step forward.
If you've never used a 4G modem, you'll be struck by how much faster the 4G system is than Sprint's previous 3G. Using the speedtest.net Web site, I got download speeds averaging around 800 kilobits/sec on 3G, but averaging more than 3 megabits/sec and peaking at 5.6 megabits/sec on 4G. That's still much slower than the average of 6 megabits/sec Sprint advertises for 4G, which has been a perpetual problem for Sprint. But it's a huge boost over 3G, and it made full-screen streaming video play smoothly on my Windows 7 laptop.
Some of those advantages are dulled by Sprint's SmartView connection manager, which is an utter abomination. The PC version of this software is just plain bad. It takes ages to load, it crashes, and buttons sometimes don't seem to respond. You can get around using SmartView by connecting using the network connections icon in your task bar. The Mac version, which also works with the 250U, seems to be speedier and more stable.
Sprint right now has a bunch of modems, and the 250U is the best of the bunch because it does both 3G and 4G networks. All of Sprint's other modems are either 3G or 4G only, except for the Sierra Wireless Overdrive ($149.99, ) mobile router. You'll want the Overdrive if you tend to connect more than one device to the Sprint mobile Web, such as adding an iPod touch ($199-399) to your connection. But the Overdrive is much bulkier than the 250U, which makes the 250U the best bet for hooking a single laptop or desktop PC up to Sprint's network.