Mobile network providers must provide telephone number portability for contract customers as well as for prepaid customers. The subscriber is entitled to request porting his telephone number at any time. The subscriber no longer needs to terminate the contract with the previous provider to do so. When porting the telephone number without terminating the contract, the mobile customer is obligated to continue paying the fees for the old and, if applicable, the new contract with a different provider. A new mobile number can be assigned to the old contract.
Whilst in the past it was possible to identify the carrier by the mobile prefix and the charges may be incurred, this is no longer the case due to the mixed range of numbers portability creates. For this reason there are now network queries which provide the carrier the number is assigned to.