Is this what you're after? Call the O2 Top-Up lineFREE by using Hotkey 3 or dialling 4444 from your mobile phone. If you are calling from a landline call 08456 062 277 (calls charged at the local rate).Have your Debit/Credit Card numbers ready and follow the simple step-by-step instructions. You'll hear a 'Top-Up successful' message when your calltime has been credited.Cards you can use to Top-Up are Visa, Visa Debit, Visa Electron, Mastercard, Maestro and Solo.</p> You can Top-Up between £10 and £30 at a time.</p>