Cepstral Community

I bought Callie for an Industrial system that speaks alarms dialed over the phone. I thought the modem version (8kHz) would be clearer than it is. Does anyone have any tips on how to make this clearer overall? The voice is very good on the PC speakers, but not very clear on the phone. I have tried speeding her up and slowing her down, but no luck. Thanks! hvg
System is XP Pro, Modem is AOpen FM56-PX.