The AiRave works great, though the distance is about 2 walls or 50 feet. Cell only, no data.

If you're speaking via the AiRave (you hear a tone at first) you can leave the coverage and still keep the call if you still have a regular Sprint signal.

Same thing walking towards the AiRave. When you get close to it, you hear a tone and then you're on the AiRave. The call doesn't drop.

The sound quality is as good as any VoIP call. I have an excellent Verizon Fios connection. Your mileage may vary.

Cost was $99 for the Sprint Femtocell, plus $5 per month. Sounds like AT&T's is a better deal at $150 with no monthly and it includes data.