A femtocell is a small cellular base station which connects to a service provider via broadband and transmits signal. These are mainly designed for better reception in homes at offices, anything that is between four walls. Sprint won't offer it for free, but will charge US$17.99 for the Airava.

Airava femtocell provides 5000 square feet by creating a low power licensed spectrum CDMA network, and according to Sprint, it's more reliable than WiFi networking. If you don't want the US$17.99 price, you could always go for an unlimited calling plan at US$4.99 per month if you already have a contract, if not, it's US$ per month, and for families, US$20 per month.

T-Mobile already offers such a service called T-Mobile's AtHome which uses WiFi instead of CDMA.

Source: Digital Trends