US mobile phone operator Cingular has announced plans to charge a $4.99 monthly fee to customers with an old mobile phone in a controversial attempt to persuade them to upgrade.

As the network moves to a single technology it is levying the fee to 8%, 4.7 million, of its subscribers. Users with TDMA phones will be required to either pay the fee or upgrade to the GSM network that has been the standard for some years. Cingular are offering discounts on new phones to any affected customers but said it was willing to risk an increase in customer cancellations as it tries to save costs in the future.

Cingular is to shut down the TDMA network in 2008 but is required to keep it running until then by Federal Communications Commission legislation.