There's been thread after thread here each day asking the same questions; so I thought I'd post a topic which clears up and clearly explains the iPhone (i4) problems in hope that people can refer to this instead of posting another. It'll be blunt and to the point; well, you came here for honesty, right? If you feel I've posted anything misleading, please mention it - politely! 
The 3 'most complained about' problems:
1. The infamous antenna
2. The 'green blob'
3. Proximity sensor issues
The answers, and the truth about each:
Problem 1 - The infamous antenna:
Undoubtedly the most complained about 'problem' the new i4 suffers from. Very briefly, holding the bottom left corner of the phone causes a dramatic signal loss - sometimes taking full 3G signal to 'No service'. Yes, it's as bad as 'they say it is', and yes (almost?) everyone suffers from it. Now, when I say everyone, I'm including those people who don't believe that they suffer from it. Supposedly less than 7% of iPhones do not suffer from it. I for one do not experience the issue purely because I don't hold the phone (naturally) in the left corner. Experiencing the issue during normal use and your i4 suffering from the issue are completely separate things - a lot of people don't seem to understand this. I am personally yet to see first-hand, solid evidence that there are i4's out there which do not suffer from this problem. Different geographical areas/original signal strengths have an effect on how badly the signal drop occurs; but it exists - it's a fundamental design flaw.
The 'upcoming software update';
The upcoming software update will not, I repeat will not fix the problem. This update is to adjust the way the iPhone displays bars, which may make the signal appear to drop less significantly under certain conditions. The actual issue is caused by a design flaw which cannot be fixed by software updates.
The solution;
You could try waiting a few weeks/months to see if Apple slyly apply some form of non-conductive layer over the problematic area on new batches of i4's. As it currently stands, your choices are; a £25/$29 Apple bumper (or any similar case), an iPhone 3GS or an alternative phone altogether. End of.
Problem 2 - The 'green blob'(!):
Strange as this may sound, it's one of the most complained about 'problems' with the i4. If your phone suffers from this issue, in the centre(er) of any photos you've taken with the phone, you will notice a fairly obvious green tint.
The solution;
Take it back to an Apple store, explain the problem and test the replacement i4(s) in the store to avoid repeated journeys. Problem solved! Fortunately, this is an issue I haven't (yet?!) experienced.
Problem 3 - Proximity Sensor issue
A fairly self explanatory problem. The proximity sensors on the i4 seem to enable the screen when moved even slightly away from one's face. The user is then likely to inadvertently press buttons with their cheek/ear causing very random actions to be carried out on the phone mid-call - sometimes with the user completely unaware. An annoyance more than anything.
The solution;
Try to keep it close to your face. I have faith in this being fixed within a software update since it's the software deciding to enable the phone; the sensors just provide the software with data to decide from upon request. I've not personally experienced this issue either, but I naturally push the phone to my face with my index and middle fingers on the back of the phone when talking.
A quick conclusion:
The i4 has suffered a lot of abuse from huge media corporations and, perhaps more importantly, the public. Regardless of whether or not Apple should've stuck with an internal antenna, what's done is done, and the i4 is on the shelves in this state. They've admitted to the problem, and AppleCare have admitted that they can't fix it. You can either live with it, or you buy a different mobile. It really is that simple at present. I'm sure in the near future, someone somewhere will come up with a viable solution (maybe even Apple) - but it's going to be a physical component, not a software update. It's disappointing from Apple, but they're even getting good at that now.
The i4 has its flaws, but in my honest opinion (owner of one for 4 days), it's one of the best pieces of kit I've ever used. If you're lucky enough to naturally avoid holding the antenna (bottom left corner specifically), I would strongly suggest getting yourself one of these new toys. You have 30 days grace upon purchase, so bare that in mind if you want to give one a try. If you don't like it, return it, or perhaps check out eBay for a nice profit.
Best of luck to all of you suffering from any issues.
Kindest regards,
Andy
The 3 'most complained about' problems:
1. The infamous antenna
2. The 'green blob'
3. Proximity sensor issues
The answers, and the truth about each:
Problem 1 - The infamous antenna:
Undoubtedly the most complained about 'problem' the new i4 suffers from. Very briefly, holding the bottom left corner of the phone causes a dramatic signal loss - sometimes taking full 3G signal to 'No service'. Yes, it's as bad as 'they say it is', and yes (almost?) everyone suffers from it. Now, when I say everyone, I'm including those people who don't believe that they suffer from it. Supposedly less than 7% of iPhones do not suffer from it. I for one do not experience the issue purely because I don't hold the phone (naturally) in the left corner. Experiencing the issue during normal use and your i4 suffering from the issue are completely separate things - a lot of people don't seem to understand this. I am personally yet to see first-hand, solid evidence that there are i4's out there which do not suffer from this problem. Different geographical areas/original signal strengths have an effect on how badly the signal drop occurs; but it exists - it's a fundamental design flaw.
The 'upcoming software update';
The upcoming software update will not, I repeat will not fix the problem. This update is to adjust the way the iPhone displays bars, which may make the signal appear to drop less significantly under certain conditions. The actual issue is caused by a design flaw which cannot be fixed by software updates.
The solution;
You could try waiting a few weeks/months to see if Apple slyly apply some form of non-conductive layer over the problematic area on new batches of i4's. As it currently stands, your choices are; a £25/$29 Apple bumper (or any similar case), an iPhone 3GS or an alternative phone altogether. End of.
Problem 2 - The 'green blob'(!):
Strange as this may sound, it's one of the most complained about 'problems' with the i4. If your phone suffers from this issue, in the centre(er) of any photos you've taken with the phone, you will notice a fairly obvious green tint.
The solution;
Take it back to an Apple store, explain the problem and test the replacement i4(s) in the store to avoid repeated journeys. Problem solved! Fortunately, this is an issue I haven't (yet?!) experienced.
Problem 3 - Proximity Sensor issue
A fairly self explanatory problem. The proximity sensors on the i4 seem to enable the screen when moved even slightly away from one's face. The user is then likely to inadvertently press buttons with their cheek/ear causing very random actions to be carried out on the phone mid-call - sometimes with the user completely unaware. An annoyance more than anything.
The solution;
Try to keep it close to your face. I have faith in this being fixed within a software update since it's the software deciding to enable the phone; the sensors just provide the software with data to decide from upon request. I've not personally experienced this issue either, but I naturally push the phone to my face with my index and middle fingers on the back of the phone when talking.
A quick conclusion:
The i4 has suffered a lot of abuse from huge media corporations and, perhaps more importantly, the public. Regardless of whether or not Apple should've stuck with an internal antenna, what's done is done, and the i4 is on the shelves in this state. They've admitted to the problem, and AppleCare have admitted that they can't fix it. You can either live with it, or you buy a different mobile. It really is that simple at present. I'm sure in the near future, someone somewhere will come up with a viable solution (maybe even Apple) - but it's going to be a physical component, not a software update. It's disappointing from Apple, but they're even getting good at that now.
The i4 has its flaws, but in my honest opinion (owner of one for 4 days), it's one of the best pieces of kit I've ever used. If you're lucky enough to naturally avoid holding the antenna (bottom left corner specifically), I would strongly suggest getting yourself one of these new toys. You have 30 days grace upon purchase, so bare that in mind if you want to give one a try. If you don't like it, return it, or perhaps check out eBay for a nice profit.
Best of luck to all of you suffering from any issues.
Kindest regards,
Andy