I just did it! Must have Jailbroken iphone and iFile or SSH and depends what carrier u used before giffgaff. For 02 network I did with iFile: Sytem/ Library /Carrier Bundles / Iphone/ then scroll down to your carrier, mine was O2_UK.bundle/ carrier.plist then edid with text viewer and look for VoicemailPilotNumber under this there is a key 9011 needs change to 443, then scroll down again untill u see another 9011, change again to 443 then save and reboot. 🙂
This works. Thank you.
I'll give detailed instructions in the hope that they make this fix more accessible.
First of all you'll need your iPhone and a computer connected to a wireless network. You can do this without using a computer by using the 'iFile' app which you can download from Cydia, but that's not the method I'm detailing here.
1. Jailbreak your iPhone. To do this go to the following webpage, find your iPhone model and click the link. This will take you to an easy step by step guide to jail breaking:
6. Now you need to use the application you downloaded in step 5 to connect the iPhone. Here I'll give specific instructions for using Cyberduck with the Mac, but you should easily be able to adapt the instructions to WinSCP:
Launch Cyberduck and Select 'Open Connection'. Then select 'SFTP (SSH File Transfer Protocol)' from the drop down menu. The port number will change to port 22. In the 'Server' field type the IP address of your iPhone whih you wrote down earlier. In the 'Username' field type 'root' without the quotes. In the 'Password' field type your password. If you didn't change this in step 4 your password will be 'alpine' without the quotes. Then click 'Connect'.
7. In the drop down menu change the address from '/private/var/root' to '/'. Then navigate through the directories: System | Library | Carrier Bundles | iPhone | O2_UK.bundle
8. Drag and drop the 'carrier.plist' file to your desktop. Make a back up of this file just in case things go wrong.
9. Open the file with TextEdit. If you're using WinSCP in Windows use WordPad instead. Much of this text file will look like gobbledygook but don't be intimidated by that.
Search the file for '9011' without the quotes and change this number to 443. Only change the number, don't change any of the adjacent text.
Then search the file for '901' without the quotes and also change this to 443. Again, only change the number, not any of the text.
Now save the file and close TextEdit.
10. Drag and drop the edited file from your desktop back into the 'O2_UK.bundle' directory. Tell Cyberduck to overwrite the file when asked. Now click 'Disconnect' and Close Cyberduck.
11. Reboot your iPhone. Do this by holding the top right button and until you are presented with the option of turning the iPhone off. Turn it off. When the screen has gone completely blank turn it on again by holding the same button.
Now the Voicemail button should work 😉