You can check your balance by calling 444 or by going to My3 on your phone or computer.
To check your balance on your Three phone call 444 or 0843 373 4444 (5p per minute from a BT landline, other networks may vary) and select option 1. Calling 444 is free from your Three mobile.
If you haven't registered with My3 yet, you can register straight away here. If you're already registered, you can go straight to My3 to check your balance. You'll see the number of text messages you have left as well as the expiry date for free texts and internet data. If you're on 3Pay you'll also see the expiry date for your Three-to-Three calls.
To check your balance using My3 on your Three phone: