Here is some info on the iPhone:
How to Disable Safari
The iPhone OS is equipped with a "Restrictions" feature which allows you to password protect certain applications. Go to Settings -> General -> Restrictions and you can create a password for Safari. You can then forget this password and give it to someone else. If you happen to know it and want to reset it, type in the password, then disable restrictions and re-enable it. It will ask you to type in a new passcode. NOTE: Restricting Safari will prevent you from using Safari at all, even for safe content, unless you know the password. If you need your browser for safe activities, see below.
Setting up Mobicip
There are now a number of filters available for the iPhone. I use Mobicip which is excellent and only costs a few dollars. Basically, you download the app and use it to browse instead of Safari (which should be disabled). You set up an account by pressing the Mobicip app for the first time. Select the option to create a new account. Enter an email address that you do not have access to and choose a password that you won't remember BUT REMEMBER IT TEMPORARILY. You will need to enter it to log in for the first time after the account is created. Set the filter level to Elementary School Level (which is the default). After creating the account, log in using the email and password you just created. Now you can safely forget the password. You will use this app to browse the web securely from now on. If you have to make changes to the settings, you will need to ask the person who's email is on the account to log into www.mobicip.com to change settings.