Sprint's SmartView software shows the network's signal strength with vertical bars. The modem can switch between 3G and 4G service in a few seconds, but only if you tell it to -- there's no automatic switching. There are some mobile creature comforts, such as online coverage maps, GPS (which works only with a 3G connection) and something called the Digital Lounge for downloading apps, music and games.
Unlike most other USB modems, the 250U has jacks to connect an external antenna for better reception. Sierra Wireless says its $35 Band Blade Antenna, for example, can boost the signal by up to 50% and works with both 3G and 4G networks. (I didn't test an external antenna for this story.)
The final pieces of the 4G puzzle are the service plans that Sprint offers. I used the $60 4G/3G Mobile Broadband Connection Plan, which includes unlimited use of 4G data but limits 3G usage to 5GB per month. In one of the few high-tech bargains available today, it costs the same as Sprint's 5GB-per-month 3G-only plan.
Sprint also sells a $50-per-month 4G-only plan, but with that option you lose the 3G safety net. Infrequent travelers can pay $10 for 24 hours of unlimited 4G service.
To gauge Sprint's 4G network, I tested it in and around New York City, where commercial service started in early November. First, the good news: It's fast. Really fast.
The 4G network delivered an average download speed of 4.1Mbit/sec. -- about what you'll get with a wired DSL or cable modem connection. It was seven times faster than Sprint's 3G service, which averaged 550Kbit/sec. I received a peak 4G download speed of 11.2Mbit/sec. at one location, nearly 10 times faster than the 1.2Mbit/sec. of throughput available on Sprint's 3G network at the same location two minutes later.
In other words, forget about having to go to Starbucks or a public library to download that huge file you need.
Now for the bad news: I found uploading data painfully slow on both services. While 3G mustered a 25Kbit/sec. throughput from notebook to server, 4G was able to move 41Kbit/sec. -- not a terribly significant improvement. Clearly, this service is more useful for downloading large chunks of data, such as monster spreadsheets, videos and presentations, than for tasks such as uploading content to a Web site or sending e-mails bulging with attachments.