If there is an existing user on the account that would like to have their number changed, a request can be submitted through your account manager or here. A number change does not reset the contract.
An example of requesting a number change – a person is receiving harassing calls.
A number replacement is slightly different. If the company decides to remove a number from the account during the contractual period, they are obligated to pay the subscription fees for the remaining months. However, a new number can be added to the account in place of the existing number to complete the duration of the contract thus avoiding penalty fees.