If you receive an e-mail or an SMS message to your cell phone from an unknown source instructing you to dial a number beginning with the digits 899, beware: the call could cost you as much as 10 and maybe more. Easily confused with the 800 prefix denoting toll-free numbers, 899 numbers allow for part of the inflated cost of the call (usually around 50 per cent) to be credited to the number being dialled. Other numbers to watch out for include those beginning with the prefix 144 or 166. For information and to deactivate such numbers from your land-line phone, contact Telecom Italia on freephone 187.