A modem uses information from prior calls in a current call if the current communication line is similar to the communication line of a prior call. During modem training, the current communication line is compared to a communication line used during at least one prior call. If the characteristics are substantially similar, stored data mode information from the prior call(s) is used to design a signal constellation for use during the current call's data mode. If the number of prior calls exceeds a value, then the signal constellation may be designed using previously stored data mode information without using information from the current call's training mode. If the number of prior calls does not exceed the value, then the signal constellation may be designed using the previously stored data mode information and information from the current call's training mode.