A radio access network (RAN) may receive a call setup request from a wireless communication device (WCD). The call setup request may indicate that the WCD supports a first media codec. The RAN may obtain a set of candidate wireless coverage areas for serving the WCD. A first subset of the candidate wireless coverage areas may support the first media codec, and a second subset of the candidate wireless coverage areas might not support the first media codec. The RAN may assign traffic channels to the WCD, such that the assigned traffic channels include traffic channels from at least two of the first subset of the candidate wireless coverage areas, but do not include traffic channels from any of the second subset of the candidate wireless coverage areas. The RAN may communicate with the WCD substantially simultaneously via the assigned traffic channels using the first media codec.