According to Three.co.uk, there are a number of ways to keep yourself or a friend topped up. If you're topping up your tablet, Mobile Wi-Fi or dongle, you'll need to top-up in My3 or on the web.
The fastest way to top-up is through your My3 account, which allows you to register a credit/debit card for quick future top-ups. To do this you’ll need to log in to My3 or register if you don’t have an account.
To register a credit/debit card and top-up, select Top-up your account from the My3 homepage, then select the Credit/debit card tab and Register this card for future use on the payment screen. You can also register a card by going to the Manage cards section of My3 and selecting Add card.*
To make a one-off card payment, simply fill in your payment details or select the One-off payment option.
To top-up by voucher, select Top-up your account from the My3 homepage, then select the Voucher tab and follow the instructions to top-up.
You can top-up a friend’s account by logging into your My3 account and selecting Top up another account in the Top-up section.
You can also top-up on the web without registering a card or logging into My3, you’ll just need to re-enter your details each time you top-up.
Once logged in, enter the number you’d like to top-up, select Credit/debit card or Voucher, then follow the on-screen instructions to top-up.