Have someone call you from a number not on your phone, bet it works fine. Check your contact info and you probably have a ringtone that is no longer on your phone assigned to the person. I assigned a standard ringtone on the contact and now it works fine.
Phone seems to have a delay issue with a contact having a ringtone not on phone.
If you have the same problem with multiple phones you need to try this:
Have someone else try your slider on in incoming phone call and see if the have the same results. Your screen senses your touch and reacts. Might sound stupid but maybe your skin temperature is outside the limits at time. Can't think of another reason why you could have this periodically on different phones that you have tried.
I have the problem as well. Slide to answer works only sporadically. Sometimes doesn't slide at all. Sometimes only halfway and then springs back. (And this is only an issue with "Slide to Answer" for incoming calls. "Slide to Unlock" works fine.)
With all due respect to the good people offering suggestions, this is not a hardware issue, nor is it human error or dirty hands. Our phones (mine at least, can't speak for everyone) have never been dropped, never gotten wet and have never been jailbroken.
I currently have an iPhone 4, but the problem existed on my iPhone 3GS as well, as well as a previous iPhone 4 that had screen issues. I have tried restoring the phones and, with each new one, always begin as a new phone, never a backup of an older one. It also occurs with both iOS4 as well as OS3.
Because of this, I can only think of two possible causes: 1) A downloaded App that is making the problem occur, or 2) Something within my iTunes that is making this one feature glitchy.
I'd be curious what apps others have on their phones. Maybe we can find a common denominator.
Here are mine:
Record, NotifyMe, Dropbox, MusicID, Slingplayer, DVR Remote, XM Radio, iHandy Level, Appzilla, Chase Mobile, Citibank Mobile, Flixster, IMDB, ebay, Open Table, CNN, AP Mobile, Angry Birds, Skee-ball, Doodle Jump, Fruit Ninja, Downhill Bowling, Labyrinth 2, Words with Friends, Backgammon, Sudoku, Apple Texas HoldEm.
I should also mention that I have thousands of photos from my iPhoto library. Not sure if this could have an effect.
I've pretty much scoured the internet, and nobody has a good solution yet. Any help appreciated.
I have the same problem with my new iPhone 4. Sometimes the slide to answer will not move at all. Once it moved half way then jumped back (i tried several times).
I have the updated iOS 4.0.1, I didn't have that problem with 4.0 but then I didn't have that version for long.
This problem is very annoying as it makes me look ridiculous trying to answer a call and having to drop it in the end.
This is only with slide to answer, never with slide to unlock or to switch off.
I think it has always happen when someone in my contact list was calling.
Need a solution quickly !
I have the exact same problem.
It happens about 1 call over 4, so it is very often and extremely annoying. I'm thinking of getting a full refund because of this. It literally makes the phone unusable. This is a much more important problem then the antenna problem.
The exact problem (on iPhone 4 (MC603FB) with iOS 4.0.1 (8A306)):
The phone has to be in lock mode (screen turned off). Then I get a call and the slide to answer arrow appears (it can be someone from my contacts or not) and the green arrow simply doesn't move at all ! Not a single pixel, just like if the screen was dead. Then when the phone stops ringing, the message missed call appears with the slide to unlock below. And here again, the slide to unlock just won't move at all ! But I just press the power button twice (screen goes off then back on) and the slide to unlock works perfectly without a single glitch. I have tried several times, the slide to unlock doesn't move at all and I press the power button twice and it slides without problem (this is systematic). The slide to unlock hangs ONLY after having a call that I cannot answer. If I press the power button or home button while the phone is lock, then the slide to unlock always works, I never had the problem in other cases.
@msedaka: I don't have any of the apps you have. But I have a lot of others (59). I also have photos but only 247 (5 songs and 4 videos).
For info: I am in France using Bouygues Telecom.
In my opinion this is absolutely not a hardware problem (neither dirty finger problem): because if a press the power button twice immediately after having the problem, the problem goes completely away, also I have never dropped the phone. It does not have something to do with contact info or option having to load or anything because I have this with people from my contact or not. It does not have something to do with the signal strength either: I had the problem even with full signal strength. Pressing the home button doesn't help. Also I cannot refuse the call by pressing the power button while having this problem, but right after the call is missed I can press the power button to turn off the screen.
If someone from Apple reads this: please ask me for any other details and / or ask me to do some tests that I will do the next time I have the problem. I am really willing to help because this is a major problem of the iPhone that seems to exist since a long time (I'm saying this from what I see on forums, not my own experience (I only have an iPhone 4, and only since one month)). I am myself a developer so I know what can and cannot be the source of the bug. I will continue to make tests over this problem and report them here.
It would be good if the other peoples having this problem reports more details (does the power button works to refuse call? does the green arrow move a bit or not at all? what signal strength did you have at this moment? can you slide to unlock once the call is missed? if not, does it help to press the power button twice? does it happens with people only from your contacts or everyone?)
Thank you for your consideration of this major problem.
I have seen this problem. I think it has to do with temperature differential. I'm guessing the phone is in my pocket heating the screen to body temperature and pulling it out to answer there is not enough energy differential for the screen to feel the finger swipe.
The problem probably goes away after the glass warms in the air for a few seconds, but when answering we pull out the phone and swipe. That's just a guess.
The point is I too have seen this problem and it is very frustrating to miss a call because of the finger swipe issue. It would be nice if there was a hard button way to answer and ends calls.
Although I enjoy apple products, if the phone stops being a good phone, then all the other stuff is nonsense and I'll have to get another product. This and the speakerphone-only issue are two strikes against this phone.