Sprint's 3G network is painfully slow. Its old 4G WiMAX network has been punted over to Virgin and Boost. But if our exclusive test results hold up, its new 4G LTE network will be competitive with AT&T's and Verizon's.

We got early access to Sprint's network at five locations in the Atlanta, Georgia area during the week of June 11, and ran speed tests on a specially provisioned LG Viper 4G LTE phone using both our own Sensorly speed test app and the Ookla Speedtest.net app.

Sprint's results are fast, although they're not as fast as the peak speeds we've seen from AT&T and Verizon. That's because Sprint is using 5MHz channels rather than the 10MHz channels the other carriers are using in most cities. If you compare Sprint's speeds to four cities where AT&T is using 5MHz channels (Charlotte, Chicago, Los Angeles, and Raleigh), Sprint is extremely competitive.

It's not a totally fair comparison, of course. For our Fastest Mobile Networks project, we tested ordinary retail phones on loaded networks, and we didn't tell the carriers where we were going in advance. For this Sprint test, we used phones tuned by Sprint's engineering team at pre-approved locations. They knew we were coming.

Sprint's LTE Speeds: The Results

Sprint's LTE network is faster than its old WiMAX network. It's a bit faster than T-Mobile's HSPA+ 21, and it's about 25 times as fast as Sprint's 3G network. But it doesn't quite match AT&T's and Verizon's LTE speeds in cities where they have more spectrum.

Sprint execs have said they're aware of this, and that the carrier is going to be focusing on providing a great average experience in loaded conditions rather than very high peak speeds.  I've been hearing this from several wireless carriers recently: It's better to have a high floor than a high ceiling. Users notice when connections drop down to 1Mbps much more than they notice the difference between 8 and 15Mbps.

A consistent experience is really what people want, of course, but we'll have to see if Sprint pulls it off when it actually has a retail network.

Now to the numbers.

The two speed tests we use return very different results; it's just the way they were designed. Ookla's test tends to give faster numbers because it eliminates some slower results and runs multiple transfers simultaneously. Sensorly's test runs one stream at a time and don't eliminate any results. We consider the Sensorly test more realistic because smartphones usually queue large data transfers rather than running them in parallel; Web pages do consist of multiple small transfers in parallel, but time-to-first-byte plays a larger role there than peak speeds.

That said, what you want to look for with any test is relative results, not absolute numbers. What matters is how different networks compare on the same test.

Using the Sensorly software at four of our locations, we got average download speeds between 9 and 13Mbps, which is similar to the speeds in AT&T's two faster 5MHz channel cities but slower than you see in its 10MHz channel cities. Sprint's peak download speeds hit 26.5Mbps down, which is as much bandwidth as anyone really needs. That's also similar to AT&T's peak speed in a solid 5Mhz city like Raleigh, where we got a 27.8Mbps peak on AT&T.

Sprint's download speeds were comparable to speeds on Verizon, which uses 10MHz channels, but Verizon also has many more people using its LTE network.

Uploads were on the slow side, but here's where the test method really becomes an issue. Using our Sensorly test we saw upload speeds averaging 2.19Mbps, once again comparable to AT&T's 5MHz cities and faster than T-Mobile's HSPA+ or Sprint's old WiMAX 4G, but slower than Verizon. The network hit 2.97Mbps for peak uploads.

But I'm pretty sure both Sprint and AT&T are tuning their networks to respond better to multiple simultaneous upload streams, because when Ookla tested four streams at once, we saw 7.4Mbps up on Sprint. AT&T has shown a similar difference in upload speeds when tested with the Ookla software in the past.

What This Means for Sprint

Sprint has already been selling LTE phones for a while. The LG Viper 4G, Samsung Galaxy Nexus, and HTC EVO 4G are all LTE-enabled. The carrier has stopped selling WiMAX phones to its postpaid customers, so it's LTE or nothing at the moment.

Sprint has said it will launch LTE in six cities around midyear (that's the end of this month). Those cities are Atlanta, Baltimore, Dallas, Houston, Kansas City, and San Antonio. The rest of Sprint's network will get LTE by 2014, but Sprint isn't saying who'll get it when, between now and then.

This phase of LTE is just the first step in a long roadmap for Sprint, which includes increasing channel sizes using future LTE-Advanced technology and supplementing its speeds with Clearwire's upcoming LTE-TDD network.

Hopefully, the arrival of LTE will also take some pressure off of Sprint's 3G network. In our nationwide tests, Sprint's 3G system seemed hammered, with half the average download speed of Verizon's 3G. (The two carriers use the same technology.) That will help Sprint iPhone owners with their 3G-only devices.

But not knowing when LTE is coming is a big problem for Sprint customers. The carrier's 3G network is the slowest of the major wireless providers, and even high-end phones like the new EVO 4G LTE are stuck on 3G for now. Sprint has to provide more clarity quickly on where LTE is rolling out or risk losing high-end smartphone users to LTE networks that actually exist.