Even though Sprint was one the first carriers in the country to offer a femtocell solution to its customers, its Airave device was not able to support 3G service. So while your voice calls would improve, your data signal would be the same as before. (The Airave does provide coverage for the 1x network, however.)
Now it seems that Sprint will finally be adding 3G/EV-DO support to a new generation of Airave femtocells, including a port for landline VoIP, if these FCC documents are to be believed. Word is that Verizon is also getting in the game by releasing a 3G femtocell later this year as well (Verizon calls its femtocell a Network Extender). This is hot on the heels of AT&T announcing that it'll be rolling out its 3G Microcell device nationwide starting this month. Neither Verizon nor Sprint have responded yet to our inquiries for confirmation.