This page explains how to set up TiVoToGo. Unfortunately it is not yet available on all TiVo units.

You can request to be placed on a priority list to have the new software sent to your TiVo. Your TiVo service number must begin with 110, 130, 140, 230, 240, 264, 540, or 590 in order to be eligible (at this time).

TiVo.com | How to get TiVoToGo