Put the settings in manually.
This method is valid for all versions of iOS including iOS7
Step 1: Firstly, check whether you have an old profile. Head to Settings > General > Profile. If you can't see "Profile" move on to step 2. If you can see an old giffgaff profile, tap it and press "Remove".
Step 2: Go back to Settings > General and press "Reset". Don't worry, this doesn't delete any of your personal belongings.
Step 3: Hit "Reset Network Settings" and follow through. Note that this will delete your WiFi passwords! You may need to enter your passcode, at which point your iPhone will reboot.
Step 4: Go back to Settings > General > "Mobile Data" or "Network" (depending on your iOS version). For IOS7 Go to Settings > Mobile
Step 5: Tap "Mobile Data Network". Now under "Mobile Data" enter:
APN - giffgaff.com
Username - vertigo
Password - password (this should already be entered by default)
Leave Visual Voicemail as it is.
Step 6 (Almost there): Scroll down. Under MMS enter:
APN – giffgaff.com
Username – vertigo
Password – password (again, this is the default)
MMSC – http://mmsc-ac.mms.o2.co.uk:10021/mmsc
MMS Proxy: 126.96.36.199:8080
MMS Max Message Size - 2097152
MMS UA Prof URL (just leave blank)
Do NOT press the " Reset Settings " button when you’ve done this.
Once the settings are in, turn your iphone off ( via the red slider ) till the screen is completely blank. Then reboot. If you do not see the apple logo, the settings will not stick.
Then, press “ Settings “…“ Messages “ and ensure that " MMS Messaging " button is set to ON.
In " settings " " messages " turn imessages on.
Please also ensure that the " Enable 3G " button and the " Mobile Data " button are set to ON. (Press Settings, then General, then Mobile Data, or for IOS 7 Press Settings, then Mobile)
Then " Settings " ... " Phone " .... And check " My Number " is correct
Go to " Settings " ... " Carrier " and change to O2-UK.