Methods and messages for performing assignment and activation of voice bearer channels for mobile stations (MSs) in an unlicensed mobile access network (UMAN). URR (UMA radio resource) channel activation messages are exchanged between an MS and a UMA network controller (UNC) operating in the UMAN to assign a voice bearer channel to the MS and verify the channel is available for uplink. The MS may access the UMAN via a wireless access point (AP) that is communicatively coupled to the UNC via an IP network. The URR channel activation messages are sent between the MS and the UNC using an Up interface comprising a set of layered protocols over an underlying IP transport.