In conventional cognitive radio networks it is usually assumed that the primary network remains unchanged. The onus is then placed on the secondary network users to make the best use of any residual radio capacity. In some situations however, the primary network operator may wish to accommodate secondary user access. This objective has motivated recent work which considers simple modifications at the primary user stations that would lead to better secondary spectrum availability. In this paper primary base station scheduling mechanisms are proposed which are designed to be friendly from a secondary network user perspective. The authors focus on packet scheduling algorithms which maximize friendliness when the secondary users are transmitting real-time VoIP traffic.