My DirecTiVo's on day 156 without a phone line (and I know this because it actually tells me the number of days since the last call in its daily nag). The TiVo works totally fine with full functionality, but I do get that nag screen every day. I believe you don't actually get it on a daily basis until after 30 days, but I'm well past that so have learned to just live with it.
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-Aaron