A method and system is disclosed for maintaining codec consistency across a communication session. When a communication session is set up for an access terminal (AT) operating in a wireless communication system, a network device, such a base station, can determine a coding rate to assign the AT for its air interface in a manner that accounts for network capacity variations spatially and/or temporally across the session. If the requested communication session is determined to be with a landline device, then a higher coding rate may be used than might otherwise be selected. If the requested session is with another AT, then a coding rate that best accommodates the air interfaces of both ATs may be used. If the AT is predicted to handoff to multiple sectors during the session, then a coding rate that best accommodates the air interfaces of all the predicted handoff sectors may be used.