[Updated below with statement from AT&T, which blames a software upgrade and says the issue has been resolved.]

We've been experiencing ongoing problems trying to connect to the Internet using AT&T's 3G network via our iPhones over the past two days. As it turns out, we're not alone. iPhone users in Seattle report sporadic service, according to messages on Twitter.

"Experiencing ATT 3G suckage since yesterday. Only EDGE seems to be working all over Seattle," wrote one user about an hour ago.

I started experiencing problems Wednesday morning in the Greenwood neighborhood, and they continued into yesterday evening in downtown Seattle. (One of the reasons I was unable to post to Twitter from the TechFlash and Ignite events last night.)

As of noon today, I was having no problems accessing the Intenet or email on the iPhone.

But TechFlash managing editor Todd Bishop -- who has been in Seattle's Belltown, downtown and International District neighborhoods today -- reports ongoing problems getting onto the Internet. The issue was resolved temporarily when Todd switched off the 3G network, moving to AT&T's slower EDGE network.

We talked to an AT&T spokesperson this morning and they said they would get back to us with more information.

In the meantime, let us know if you are continuing to have problems and what impact this is having. Obviously, this comes at a bad time for AT&T amid chatter that a Verizon iPhone may be in the works.

Update, 3 p.m.: AT&T says the problem was caused by a software upgrade, and that the problem has been resolved.

"Some Seattle AT&T customers experienced an interruption of 3G data service yesterday evening and this afternoon," the company said in a statement. "All service has been restored. AT&T is continuously working to strengthen our network to ensure the best possible experience for our customers."

The company didn't provide details on software upgrade, or specifically how it caused the outage.

But in the absence of further information, the company's statement appears to throw cold water on the theory floated by Zillow.com CEO Rich Barton that usage of Zillow's new iPhone app caused the problem. Zillow experienced an intense surge of downloads and search queries after the app debuted in the late evening Tuesday, Barton said.

Since the launch, Zillow's new app has recorded 15,666 downloads and 414,249 searches, said Barton. (He didn't have the number of downloads in Seattle, but he suspects it's high given the "hometown effect.") The app could hog an inordinate amount of bandwidth, since it includes millions of photos of homes set on aerial maps.