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We introduce a simple communication-theoretic model for phase-change memory (PCM), based on empirical observations. Our modeling effort is focused on capturing the effects of resistance drift, which is believed to be one of the major obstacles to achieving high bit/cell densities in PCM. The model is used to estimate how the information theoretic storage capacity of PCM evolves as the time gap between a write and its subsequent read widens. We use our model to evaluate the performance of simple modulation and detection schemes, also considering the use of trellis coded modulation (TCM). Our evaluation of these strategies shows that the use of TCM provides several benefits, including a significant increase in retention time, i.e., the expected maximum amount of storage time before which the stored data can be reliably retrieved.