When I wrote that it's best to buy an iPhone in September, I didn't know of the antenna and proximity sensor malfunctions.
Since then we've learned that iPhone 4 has problems with its proximity sensor; it fails to turn off the screen when it's held by a caller's face, so it's easy to accidentally disconnect. We've also learned of an antenna design issue.
The antenna problem was thoroughly discussed in one of the best iPhone reviews (see also: Gruber, Pogue, Ars)
Apple's iPhone 4: Thoroughly Reviewed - AnandTech
... The main downside to the iPhone 4 is the obvious lapse in Apple's engineering judgment. The fact that Apple didn't have the foresight to coat the stainless steel antenna band with even a fraction of an ounce worth of non-conductive material either tells us that Apple doesn't care or that it simply doesn't test thoroughly enough. The latter is a message we've seen a few times before with OS X issues, the iPhone 4 simply reinforces it. At the bare minimum Apple should give away its bumper case with every iPhone 4 sold. The best scenario is for Apple to coat the antenna and replace all existing phones with a revised model.The ideal situation is very costly for Apple but it is the right thing to do. Plus it's not like Apple doesn't have the resources to take care of its customers....
The reviewer has an engineering background (the description of the camera sensor technology is the best I've seen) and he hacked a way to measure the iPhone 4's antenna performance. Turns out that the iPhone "bars" display is almost meaningless -- anything less than 4-5 bars is a very marginal signal. Apple isn't the only company to cheat this way.
More importantly, there is a real problem with Apple's antenna design. On average it's mostly better than the iPhone 3G/3GS antenna, but to get the best results you need a case, like Apple's $30 bumper covers, to keep fingers away from antenna junctions.
The Anand team speculates that Apple goofed up on design or testing, or that they don't care. I doubt it.
I am sure Apple engineers knew about this problem. Maybe it was always a known problem, or maybe there was supposed to be a coating applied that ended up being unavailable. Most likely a problem came up not far from the release date, otherwise I think Apple would have come up with a fix of some kind.
Apple's management tried the phone, looked at the analyses, and decided to launch without a mitigation strategy. Maybe they'd been studying the Dell Way. Maybe they figured most people buy a case, most of the rest are in areas with non-marginal coverage, and AT&T customers are used to dropped calls.
They might have gotten away with it, just as they got away with blown Nichicon capacitors in the G5 iMac or the loose video cable in my i5 iMac, but the problem turned out to be even worse than they'd expected. It went viral.
Apple's still trying to tough it out, following a service script ...
1. Keep all of the positioning statements in the BN handy – your tone when delivering this information is important…
2. Do not perform warranty service. Use the positioning above for any customer questions or concerns…
4. … ONLY escalate if the issue exists when the phone is not held AND you cannot resolve it.
5. We ARE NOT appeasing customers with free bumpers – DON’T promise a free bumper to customers.
The pressure is building though, so I think Apple will do something to appease us. I think they'd be fine if they offered to sell the bumpers with an iPhone for $10 instead of $30, and give a $20 App Store voucher to current i4 owners. (They may not have enough bumpers to go around though.) Really the phone should ship with the bumpers, but they don't look so good in demos.
By the time I buy in September, I expect Apple will have fixes for the antenna and proximity sensor bugs. Honestly, September is the time to buy.