Some users have reported a yellow discoloration of the screen, which was attributed to the glass lamination glue that was used. It did not have time to dry fully before the unit reached consumers due to the speed of manufacturing.[49] Another issue reported by some users within days of the iPhone 4 release was that during calls the proximity sensor can be insensitive, so that facial contact with the touchscreen can end calls, mute calls, and dial other numbers.[50]

Antenna

Shortly after the iPhone 4 was launched, some consumers reported that signal strength of the phone was reduced when touching the lower left edge of the phone, bridging one of the two locations which separates the two antennas, resulting in dropped calls in some areas with lower signal reception.[51][52][53] In response, Apple issued a statement advising that customers should "avoid gripping [the phone] in the lower left corner" when making or receiving a call.[54]

As a consequence of this problem, it was reported on July 2, 2010 that several iPhone 4 users were planning on suing Apple and AT&T for fraud by concealment, negligence, intentional misrepresentation and defective design. The legal challenge was started by California law firm Kershaw, Cutter and Ratinoff, who set up a website to recruit disenchanted iPhone 4 buyers for a lawsuit against Apple.[55][56] Later that day, Apple issued another statement stating that it had discovered the cause of the "dramatic drop in bars".[57] Apple explained how the formula it used to calculate the number of bars to display was "wrong". Apple promised to correct the issue and release a software update within a few weeks that would address the "mistake", which had been present since the original iPhone.[57] The New York Times commented that "the failure to detect this longstanding problem earlier is astonishing."[58]

Consumer Reports initially stated that the iPhone 4's signal issues are not "unique, and may not be serious" and it continued to mention that signal loss is a problem that is faced by the entire smartphone industry. It has been such a problem that Apple made a formal apology. The next day, Consumer Reports altered their stance after encountering instances of dropped calls.[59] Consumer Reports rejected Apple's explanation after conducting tests in a controlled environment, and comparing the results against previous generations of iPhone. It sarcastically pointed out that using a piece of tape to cover the lower left antenna gap was one way to fix the problem, but recommended that consumers who "want an iPhone that works well without a masking-tape fix" purchase the iPhone 3GSinstead.[60] Consumer Reports also tested the iPhone 4 whilst it was wearing a Bumper, a frame-like cover manufactured by Apple that prevents direct contact with the antenna, reporting that it does fix the problem.[61] CNN repeated Consumer Reports' statement that a small amount of duct tape had proven an effective fix to the iPhone 4's dropped call issue.[62]

On 16 July 2010, at a press conference, Steve Jobs announced that Apple would provide all iPhone 4 owners with a free case to help solve the antenna issue and a refund to those users who had already purchased a Bumper. The free case offer would be valid until 30 September 2010, when Apple would reevaluate the situation.[63][64] To get a free case, owners were able to apply via an app installed on the phone found in the App Store from 22 July 2010 to 30 September 2010. Jobs also announced that Apple could not produce enough Bumpers for all owners of the phone, but would source a supply and offer a range of cases.[65] Additionally, Jobs cited figures from AppleCare which showed that only 0.55 percent of all iPhone 4 users have complained to the company about the issue, while the number of phones returned to Apple was 1.7 percent – 4.3 percentage points less than the number of iPhone 3GS models that were returned in the first month of the phone's launch.[65]

Consumer Reports noted that the solution was not permanent, though a good first step.[66] However, because Jobs did not specify a time line for fixing the problem, and the offering for a free bumper only being a temporary solution, PC World decided to remove the iPhone 4 from its "Top 10 Cell Phones" chart and reassign it to a pending rating.[67]

AnandTech researched iPhone 4 antenna and identified that its outer construction provides 5–9 dB (6.9–9 times) better sensitivity comparing to common internal antenna design of iPhone 3Gs (the phone keeps working connection with signal as low as −120/121 dB comparing to usual −113/115 dB).[68]

Despite the negative media attention regarding the antenna issues, 72% of iPhone 4 users say that they are "very satisfied" with their iPhone 4 according to an August 2010 survey by ChangeWave Research.[69]

Camera image fault

Reports about iPhone 4 cameras being rendered useless by a peculiar fault started to show up on the Internet in September 2010. Under certain lighting conditions the back camera produces a large green 'halo' in the center of the image.[70] This renders many of these images to be of much lower quality than what the iPhone 3GS is capable of producing under similar lighting conditions. Reports started surfacing on forums and have since been picked up by major media sources.[71]