Because your iPad can't receive text messages, you won't be able to register your My3 account. You'll be able to access it when you're connected to the Three network. It's free to access, so you don't need to worry about being charged.
You may need to turn off Wi-Fi before you visit your My3 account. Here's how:
Note: You won't be able to change your address, marketing preferences or EU data roaming limits as these settings are password-protected. If you're asked to enter a password at any time, give us a call on 0333 300 0500 (standard rates apply) or 500 (free) from a Three phone and we'll change these settings for you.