Cashback by redemption gives you money back (usually by cheque) on your mobile phone contract at defined periods throughout your contract. You will be required to send certain bills in to the retailer and once they have been received they will send out a cheque. You may receive a single cheque or multiple cheques over the duration of your contract. If you do not send in your bill within the defined period you may lose your right to claim your cashback by redemption.
Mobile phone contracts that offer free or discounted line rental usually operate in this way. You can remove these deals by ticking "no" under the "Cashback by redemption?" question in the search box.