Why push notification has delay on iPhone 4?

The order means nothing.

Mail is pushed if the mail account supports push. If not, then it has to be fetched. This can either be manual or set at a time limit, based on settings in the phone. You need to know the type of mail account you have and if it supports push, since all don't. Push has to be turned on as well.

As far as the messasging apps, it depends on the app. However, they all need to be configured to push, and that is done in settings. Go in there and set the push notifications for Facebook. Mail is in a different location.

Lately, certain mail accounts have not be pushing, and that is a fault of the mail account, not the phone. Yahoo mail is the biggest one having problems.

Okay, if you set up Gmail and Yahoo mail in the Exchange fashion, then push should work. However, there have been a number of posts on this and other forums about the failings of Yahoo push for some time now. I would believe this could be your issue with that. As far as Gmail, if you have push set up correctly in all the areas for that and it is set up for the Exchange version, it should work. I do not use either of these mail providers, so I cannot make comments based on personal experience. As far as Facebook is concerned, I would suggest turning off the notification and then turning it back on again. I use Facebook but not push notifications as it is not that important to me, however there is a section in Settings, Facebook and that sets push notifications.

If none of this corrects your Facebook issue, I suggest a restore. When connected to iTunes, you can click on Restore. Make sure you do a backup of the iPhone, you sync your contact and calendar data to the supported application on the computer and import photos from the camera roll. Try a restore from a backup first, and if that doesn't work, then a restore as a new device. Then sync information back to the iPhone from iTunes.

Yes, if you use the provided settings for Gmail, it does not support push. While Yahoo will, as I said earlier there were issues with Yahoo push.

To get Gmail to work with push, you will need to go to Google and check out the settings you need to use for the iPhone. I know there is a help topic on the Google site for this. Check this link I found off Google mobile and see if it answers your question. Once you do that, Gmail should push. Yahoo, you are going to have to wait until they get things working again.

Whoops, sorry it didn't show up. I'll try it again. Go to the first page if you want, or just go to the second link and that will give you step by step instructions. Sorry for the mixup!

http://www.google.com/mobile/sync/

http://support.google.com/mobile/bin/answer.py?hl=en&topic=14252&answer=138740