What do you do when the YouTube, Weather and Stocks apps suddenly fail to update on your iPhone but you know your Wi-Fi is working and you can use mobile Safari and receive emails? You already tried doing a “Reset Network Settings” or a “Reset All Settings” in Settings->General->Reset, and still a no go. If you just upgraded to iPhone 3.0 using any of the jailbreaking methods such as PwnageTool, Redsn0w or Purplera1n, your instinct may tell you that something went wrong and you should try and jailbreak again using the same method or tool that you used the first time or try another tool. Well, if that worked for you then your problem’s solved. If not, don’t fret. There may be an easier way to solve the problem.
Some people never bother using EDGE or 3G when they have access to Wi-Fi most of the time and they want to prevent horror stories of getting ridiculously charged by their service providers for unintended use of “data access” happening to them. Thus, they have never entered a Cellular Data Network configuration setting on their iPhone particularly for APN (Access Point Name). The APN defines the network path for all data services (Cellular Data, Visual Voicemail, MMS). Incorrect entries in the fields may disable the data services. For some reasons, this may prevent these Apple default apps from updating their data. So find out from the service provider of the SIM card you are using on what the correct settings are and enter them in Settings->General->Network->Cellular Data Network.
Modmyi.com has provided a List of Carrier APN Settings for your convenience.
Note: This screen may look different depending on the iPhone OS version you are using. Also, unless you have an unlock phone, this setting may not even be visible or editable as your service provider has already added the settings for you.
To test your setting, disable Wi-Fi and make sure you can still access the Web in Safari or send and retrieve emails. Then try Weather, Stocks and YouTube and see if they work. If they do, then problem solved. But to prevent the horror stories mentioned above from happening to you, you need to edit the APN on your Cellular Data Network settings to something else (like deleting the last character) when not using it. If you have a jailbroken phone, install SBSettings in Cydia and disable EDGE and 3G.