In one embodiment, a message is sent from the wireless network to a user equipment having a variable rate vocoder. The message defines transport block sizes for the user equipment to select from in making uplink transmissions if the user equipment is permitted to vary a packet size for uplink transmission. A scheduling grant is sent to the user equipment, and the scheduling grant includes an indicator indicating that the user equipment is permitted to vary the packet size for uplink transmissions by selecting a transport block size from among the defined transport block sizes.