Tested: iPhone 4S on T-Mobile 3G at WWDC

SAN FRANCISCO—T-Mobile has been the only national network which couldn't run iPhones at 3G speeds - until now. The carrier is "refarming" 1900-MHz airwaves to 3G, making itself finally iPhone-compatible.

Whether it's a total coincidence (as T-Mobile insists) or a publicity stunt, the carrier turned on a single 1900-MHz 3G cell site in San Francisco's Moscone West this week – the exact location where Apple will announce its new iOS 6. I took an unlocked iPhone 4S down and tested it out against AT&T and Verizon iPhones. (Sadly, I don't have a Sprint iPhone at the moment.)

The default state for an iPhone on T-Mobile is EDGE, and EDGE is really slow. I ran several tests on an iPhone on T-Mobile's EDGE network today and generally got speeds between 30-50kbps. Ouch.

But as soon as I walked alongside Moscone West, a "3G" indicator appeared in my iPhone 4S's status bar.

It's definitely a test network, using only one in-building cell site. The signal was much stronger at the front of Moscone West than at the back, and it vanished altogether half a block north of the convention center.

I ran 10 tests using the Speedtest.net app on the T-Mobile iPhone and got very erratic results; some numbers were clearly impossible, so I had to exclude them. Of the valid results, I saw download speeds from 500kbps to 6.5Mbps, but mostly in the 1-2Mbps range.

That's much less than what T-Mobile's HSPA+ 42 network can produce. On an HTC One S in the same location, I got 9.9Mbps down and 1Mbps up. And I got consistently faster speeds on AT&T, which has a slower HSPA network.

There are two factors at work here.

First, the iPhone 4S isn't capable of T-Mobile's full speeds. It's an HSPA 14.4 device like the HTC Sensation, which reached speeds of 4.3-6.5Mbps down during testing last year.

So why wasn't I getting the same 4-6Mbps on the iPhone? This was definitely a test network, and probably one designed not to emanate far outside the Moscone Center itself. Who knows what they're using for backhaul, or how much spectrum is devoted to the 1900 3G network. I wouldn't draw conclusions about future speeds from this test network.

I will draw conclusions about price, though. As I , T-Mobile's no-contract plans are competitive with Virgin Mobile and much cheaper than AT&T and Verizon, with potentially faster data speeds than any of them on 3G devices. For more on that, see .

So when will the wonders of refarming come to you? T-Mobile is remaining vague except to say that it'll arrive in a "large" number of markets this year.