Cellular Data Issues iOS 9 – simple Fix guide
There are still some users having issues with their iPhone after upgrading to the latest version of iOS 9.
This is related to wrong settings on the Cellular Data (also known as mobile data), which is the equivalent of the APN Settings on the rest of the non-apple smartphones.
 
If you just recently upgraded your phone to iOS 9 and currently not able to connect to the internet or it just gives you a slow connection, to able to connect to 3G / 4G network, you should definitely check the few suggestions below.
 
Cellular Data Issues iOS 9 – Step by Step Fix
 
First thing you should probably do is to reset your network settings.
By doing this, you will removes all network related settings, which includes store wifi network passwords and the mobile carrier parameters (APN Settings).
Your iPhone will be brought to default values and this fixes most of the cellular data related issues.
 
To do so, you need to go to Settings, Locate the General Option and then Reset. You will see an option that says Reset Network Settings – Tab on it.
 
Reset the APN – Manually configure APN Settings on your iOS 9 device.
If the above steps did not do the job, you should then try to manually reset the APN Settings on your iPhone.
 
Steps: Go to Settings, Mobile Data, Mobile Data Network and then you will see the menu where you can enter the APN, Username, etc. If you don’t have the APN Values that correspond to your mobile operator, 
 
Note: There seems to be some carriers that are restricting the access to edit the cellular data on the iPhone, if you don’t see this option in the menu, your phone has been locked by your carrier. 

Install a new profile. 

Go somewhere you can have internet access via Wifi.
​Now that you are connected to the internet, try loading a new APN profile for your iPhone using a special site.
 
Open your Safari browser, and go to m.apnchanger.org
b. Select the option ‘Manually’
c. In the ‘APN Name’ field, type: globaldata
d. Username / password: Leave Blank
e. Continue with the instructions to install the APN

The APN Settings (Access Point Names) are necessary for your iPhone 5 to be able to find to correct server from the Global Voice network, without this setup, you won’t be able to use your data plan to connect to the internet on your iPhone.  
This is the Global Voice APN Settings for your iPhone 5 or iPhone 5S

• In the main menu of the iPhone 5 tab on Settings
• Now go into General 
• Select Network.
• At this point, please double check and ensure these settings are properly set:
  • Data Roaming have to be ON in your iPhone 5 or iPhone 5S
  • Wifi: Off
  • 3G enable: On

• Go to Cellular Data Network
• The  GVC APN settings for iPhone 5 you should use:
  • APN – globaldata
  • Username – Leave it Blank
  • Password – Leave it Blank

If you cant find the option manually you can follow the next intstructions:

Automatically
Note: before making the configuration below, please make sure
your device is connected to a Wi-Fi network:
a. Dial *172# and press ‘Send’
b. Wait for an incoming SMS
c. Click on the link received in the SMS
d. Follow the instructions and install the APN

Note: Please make sure that ‘mobile data’ and ‘data roaming’ is on.
You can find it on ‘Settings’ , ‘Cellular’

*Menu names may vary regarding your device model / software version

OR

Manually
If you tried the ‘automatically’ option but did not receive an incoming SMS, you can configure the
APN settings manually.
Note: before making the configuration below please make sure your device is connected to a Wi-Fi network
a. Open your Safari browser, and go to m.apnchanger.org
b. Select the option ‘Manually’
c. In the ‘APN Name’ field, type: globaldata
d. Username / password: Leave Blank (nothing)
e. Continue with the instructions to install the APN
​
Note: Please check that ‘mobile data’ and ‘data roaming’ is on.
You can find it on ‘Settings’   ‘Cellular’