[UPDATE July 16, 2010: Apple held a press conference today addressing the issue of the iPhone 4’s antenna and signal loss. Read our latest blog: Apple to provide free cases to iPhone 4 owners —Ed.]

Apple's Bumper, a frame-like cover sold by the company to add a "dash of style" to the iPhone 4, has been flagged by some bloggers and consumers as a possible fix for the phone's signal-loss problem. We put the accessory to the test in our labs and confirmed that it does remedy the issue.

We slipped a Bumper onto an iPhone 4 and repeated our earlier tests of the phone's signal reception when held in a certain manner. Mimicking the contact described in consumer complaints about the phone, our tests measured any change in signal strength when a finger was placed over a small gap in the casing on the bottom left edge of the phone.

In the earlier tests without a Bumper, signal strength on the iPhone 4 dropped significantly each time a finger was placed over the gap, a reduction that might cause a call to be dropped. The signal problem is the reason that we did not cite the iPhone 4 as a "recommended" model, even though its score in our other tests placed it atop our latest Ratings of smart phones, released this week and available to subscribers.

With the Bumper fitted, we repeated the test procedure, placing a finger on the Bumper at the point at which it covers the gap below. The result was a negligible drop in signal strength—so slight that it would not have any effect, in our judgment.

The Bumper, a skirt made of rubber and molded plastic that fits snugly around the phone with buttons that connect to those on the device and openings for its input jacks, is sold by Apple for $29 online and at their brick-and-mortar stores. There are other third-party cases for the iPhone 4—including many that are less expensive—and presumably some of those might remedy the signal problem as well, though we haven't tested them.

The Bottom Line: The Bumper solves the signal-strength problem. So does a piece of duct tape, as we reported earlier, or just being careful how you hold the phone. But these options all put the onus on consumers to solve or pay for a fix. We're still calling on Apple to provide an acceptable free solution to the iPhone 4's signal-loss problem.

—Paul Reynolds