This article has a bit on the bottom regarding the battery backup unit, which many commenters have also mentioned. The problem is that although it is great to have broadband as well as voice calls available during blackouts, because blackouts are rare, and many homes were already in a situation where their phone was dependent on grid power, return on the investment in money and space to have the battery there can be dubious.
Once you have a battery permanently in your house, a return can be garnered by making the battery useful regardless of blackouts. A very small cheap solar panel can keep the battery charged up independently of the grid. Enough power is generated and stored to use the battery as a device charger (ipods, nintendos, mobiles etc.) that will cut your power bill considerably with no inconvenience to the utility. In my house charging devices uses a lot of electricity - not because of the amount of power required to charge the device, but because the chargers leak power all day, and the power points are hard to reach to turn them off and on each time they are needed, and the power conversion ac to dc is very inefficient. The battery/solar PV will double as an emergency charging point for devices during blackouts as well.