COS stands for Class of Service.
If you have CallPilot Voice Mail then you have 15 of them. 983 comand will do nothing good for you because does not have option for message lenth. You have to connect with crossover network cable and do changes.
Comand 983 can give you an option to change COS.
you can try COS 7 and see what heppend.

vadim
anytel