I never thought I would write any tips for using Apple products but I came across a problem when I tested VPN.ac on my girlfriend's iPad. In order to use OpenVPN from VPN.ac on iOS it requires installing an App called OpenVPN Connect. This App is not available in the China App Store. It's not possible to change your Apple ID country without adding a credit card from the country you are changing to. However you can create a brand new Apple ID for any country you want without adding a credit card. In fact you can make a new account for each country's App Store that you want to use. Just choose which account to log into depending on which Apps you need to download. Here are the steps I followed to create a new Apple ID for United States.
Step 1 - Go to this page from a computer and create a new Apple ID with an email address that has not already been used to create an Apple ID. You must use a computer, you will not get the option for no credit card if you create the new Apple ID from within your iOS device.
Step 2 - On your iOS device, open the Settings and choose iTunes & App Store, then select your current account and log out.
Step 3 - Open the App Store and try to download any App. When prompted, log in using your newly created iTunes account.
Step 4 - You will be prompted that the Apple ID has not yet been used in the iTunes Store. Choose Review.
Step 5 - Choose United States or other preferred country.
Step 6 - Scroll all the way down to the bottom of this extremely long agreement and choose agree. Take a rest if your finger gets sore before you reach the bottom. It feels like about 1,000 pages.
Step 7 - Under Billing Information choose None and then enter any US address. Make up your own, don't copy mine please.
Step 8 - When you are finished downloading the Apps from United States App Store just simply log out of the new account and log back into your original account if you need to download Apps from the China store which are not available on the USA app store.
For more information on the best VPN to use in China check here.